Theory IChO 2020

G0-1
English (Oﬃcial)

General Instruction• Only write with pen. Your calculator should be non-programmable.
• This theoretical exam booklet contains 63 pages, not including general instructions.
• This examination has 9 problems.
• You will have 5 hours to solve the exam.
• Begin only when the START command is given.
• All results must be written in the appropriate boxes in pen in the designated areas on the answer
sheets. Use the back of the exam sheets if you need scratch paper. Remember that answers written
outside the answer boxes will not be graded.
• Write relevant calculations in the appropriate boxes when necessary. Full marks will be given forcorrect answers only when your work is shown.
• The invigilator will announce a 30-minute warning before the Stop command.
• You must stop working when the STOP command is given. Failure to stop writing will lead to thenulliﬁcation of your exam.
• The oﬃcial English version of this examination is available on request only for clariﬁcation.
• You are not allowed to leave your working place without permission. If you need any assistance(broken calculator, need to visit a restroom, etc), raise hand and wait until an invigilator arrives.
GOOD LUCK!

Theory IChO 2020

G0-2
English (Oﬃcial)

Problems & Grading Information

Problem
No

Title

Total
Score

% of Total Score

1

Two Beauties of Turkey: the Van Cat and the Ankara
Cat

24

8

2

A Tale of a Reactive Intermediate

77

10

3

(±)-Coerulescine

51

8

4

Symmetry Does Matter!

66

10

5

Konya, Carrot, Beta-Carotene, Vitamin-A, Immune
System, Vision

100

14

6

Thermodynamics through an Interstellar Journey

80

12

7

Phthalocyanines

85

12

8

Boron Compounds and Hydrogen Storage

58

14

9

Quantiﬁcation of Heavy Metal Ions

100

12

TOTAL

641

100

Theory IChO 2020

G0-3
English (Oﬃcial)

Authors
ALANYALIOĞLU, Murat, Atatürk UniversityAYDOĞAN, Abdullah, İstanbul Technical University
BURAT, Ayfer Kalkan, İstanbul Technical University
DAĞ, Ömer, Bilkent UniversityDAŞTAN, Arif, Atatürk UniversityKILIÇ, Hamdullah, Atatürk UniversityMETİN, Önder, Koç UniversitySARAÇOĞLU, Nurullah, Atatürk UniversityTÜRKMEN, Yunus Emre, Bilkent University
ÜNLÜ, Caner, İstanbul Technical University
YILMAZ, İsmail, İstanbul Technical University
YURTSEVER, Mine, İstanbul Technical University

EditorSARAÇOĞLU, Nurullah, Atatürk University

Theory IChO 2020

G0-4
English (Oﬃcial)

Physical Constants and Equations−1

Avogadro's number

𝑁𝐴 = 6.0221 × 1023 mol

Boltzmann constant𝑘𝐵 = 1.3807 × 10−23 JK−1

Universal gas constant𝑅 = 8.3145 JK−1 mol

Speed of light𝑐 = 2.9979 × 108 ms−1

Planck's constantℎ = 6.6261 × 10−34 Js

Faraday's constant𝐹 = 9.6485 × 104 C mol

Mass of electron

𝑚𝑒 = 9.1093 × 10−31 kg

Standard pressure

𝑃 = 1 bar = 105 Pa

Atmospheric pressure

𝑃𝑎𝑡𝑚 = 1.01325 × 105 Pa = 760 mmHg = 760 torr

Zero of the Celsius scale

273.15 K

1 picometer (pm)10−12 m; 1 Å = 10−10 m

1 nanometer (nm)10−9 m−1= 0.08205 atm LK−1 mol−1−1

1 eV = 1.6021 × 10−19 J
1 cal = 4.184 J
1 amu = 1.6605 × 10−27 kg
Charge of an electron

1.6021 × 10−19 C

Ideal gas equation

𝑃 𝑉 = 𝑛𝑅𝑇Theory IChO 2020

G0-5
English (Oﬃcial)

Physical Constants and Equations

Enthalpy

𝐻 = 𝑈 + 𝑃𝑉

Gibbs free energy

𝐺 = 𝐻 − 𝑇𝑆
Δ𝑟 𝐺 = Δ𝐺0 + 𝑅𝑇 𝑙𝑛𝑄0
Δ𝑟 𝐺0 = −𝑅𝑇 ln 𝐾 = −𝑛𝐹 𝐸𝑐𝑒𝑙𝑙

Entropy change

Δ𝑆 = 𝑞𝑟𝑒𝑣
𝑇 , where q𝑟𝑒𝑣 is heat for the reversible process

Entropy change

Δ𝑆 = 𝑛𝑅 ln 𝑣𝑣21 (for isothermal expansion of an ideal gas)

Nernst equation

𝐶𝑜𝑥𝑖𝑑𝑎𝑡𝑖𝑜𝑛
𝐸 = 𝐸 0 + 𝑅𝑇
𝑛𝐹 ln 𝐶

Energy of a photon

𝐸 = ℎ𝑐𝜆𝑟𝑒𝑑𝑢𝑐𝑡𝑖𝑜𝑛

Integrated rate law
Zeroth-orderFirst-order
Second order[𝐴] = [𝐴]0 − 𝑘𝑡ln [𝐴] = ln [𝐴]0 − 𝑘𝑡
1 = 1 + 𝑘𝑡
[𝐴]
[𝐴]0

Arrhenius equation𝑘 = 𝐴𝑒−𝐸𝑎 /𝑅𝑇

Equation of linear calibration curve𝑦 = 𝑚𝑥 + 𝑛

Lambert–Beer equation

𝐴 = 𝜀𝑙𝑐

Theory IChO 2020

G0-6
English (Oﬃcial)

Periodic Table of Elements

Theory IChO 2020

G0-7
English (Oﬃcial)

1

H-NMR Chemical Shifts

Typical Coupling Constants

geminal2
J = 0 Hz(homotopic hydrogens)vicinalJ = 2–12 Hz(depends on dihedral angle)
32

geminalJ = 0.5–3 Hz

geminalJ = 2–15 Hz(diastereotopic hydrogens)

3

2

3

cis
J = 7–12 Hz

allylic
J = 3–11 Hz(depends on dihedral angle)
3

3

vicinalJ = 6–8 Hz

trans
J = 12–18 Hz

J = 6–9 Hz (ortho)
J = 1–3 Hz (meta)
5
J = 0–1 Hz (para)

3

4

Theory IChO 2020

G0-8
English (Oﬃcial)

13

C-NMR Chemical Shifts

Theory IChO 2020

G0-9
English (Oﬃcial)

IR Absorption Frequency Table
Functional Group

Type of Vibration

Absorption Frequency
Region (cm–1 )Intensity(stretch, H-bonded)

3600–3200

strong, broad(stretch, free)3700–3500

strong, sharp(stretch)

1150–1050

strongstretch

3000–2850

strongbending1480–1350

variable

stretch3100–3010

mediumbending

1000–675

strongstretch1680–1620

variable

C–F

stretch1400–1000

strongC–Clstretch800–600

strongC–Br

stretch600–500

strong

C–I

stretch500

strongC–H

stretch3300

strong, sharp

C≡C

stretch2260–2100

variable, not present insymmetrical alkynes

Alcohol
O–H
C–O
AlkaneC–H
Alkene=C–H
C=C
Alkyl Halide

AlkyneTheory IChO 2020

G0-10
English (Oﬃcial)

IR Absorption Frequency Table
Amine
N–H

stretch3500–3300

medium(primaryamineshave
twobands;
secondaryamineshave
one
band, often very weak)

C–Nstretch1360–1080

medium-weakN–Hbending

1600

mediumC–H

stretch3100–3000

mediumC=C

stretch1600–1400

medium-weak, multiple bands

stretch1820–1670

strong

C=O

stretch1725–1700

strongO–H

stretch3300–2500

strong, very broad

C–O

stretch1320–1210

strong

C=O

stretch1740–1720

strongC–H

stretch2850–2820 & 2750–2720

medium, two peaks

stretch1690–1640

strongstretch3500–3100

unsubstituted
two bands

bending

1640–1550

Aromatic

Carbonyl
C=O
Acid

Aldehyde

Amide
C=O
N–H

have

Theory IChO 2020

G0-11
English (Oﬃcial)

IR Absorption Frequency Table
Anhydride
C=O

stretch1830–1800 & 1775–1740

two bands

C=O

stretch1750–1735

strongC–O

stretch1300–1000

two bands or morestretch1725–1705

strongstretch3-membered - 1850

strongstretch4-membered - 1780

strongstretch5-membered - 1745

strongstretch6-membered - 1715

strongstretch7-membered - 1705

strongstretch1685–1665

strong

Ester

Ketoneacyclic

cyclic𝛼, 𝛽-unsaturated

conjugation moves absorptions to lower wavenumbers
aryl ketone

stretch1700–1680

strongstretch1300–1000 (1150–1070)

strongstretch2260–2210

mediumstretch1560–1515 & 1385-1345

strong, two bands

Ether
C–O
Nitrile
C≡N
Nitro
N–O

Theory IChO 2020

Q1-1
English (Oﬃcial)

Two Beauties of Turkey: the Van Cat and the Ankara Cat

The most beautiful of cats, the Van cat is a pure breed living only in Lake Van basin. Another endemic cat
breed is the Ankara cat. They are called Angora cats. Their most important feature is their two different
eye colors.

Just like people, cats can sometimes be stressed and angry. Just as people are made happy by melatonin,
the stress of cats can be reduced and they can be made happy thanks to a natural product. Nepetalactone
is an organic compound isolated from the plant catnip (Nepeta cataria), which acts as a cat attractant.
Nepetalactone is a ten-carbon bicyclic monoterpenoid compound derived from isoprene with two fusedrings: a cyclopentane and a lactone.

Theory IChO 2020

Q1-2
English (Oﬃcial)

Total synthesis of nepetalactone:

1.1

The above scheme describes the total synthesis
Draw structures of A–G, without stereochemical details.

ofnepetalactone.

Hints:• Compound A has strong and sharp band at 3300 cm−1 in the IR spectrum.
• A, B, and F are monocyclic, while C, D, E, and G are bicyclic compounds.
• F has one doublet at ∼ 9.8 ppm in the 1 H-NMR spectrum.

14.0ptTheory IChO 2020

Q1-3
English (Oﬃcial)

Reactions of nepetalactone:

The above scheme includes a few reactions of one of the enantiopure nepetalactone 1 isomers. Threeof the reaction products (5, 6, and J) are used as insect repellents in industry.
1.2

For the relationship between 5 and 6, which of the following is/are true? Tickthe box next to the correct answer(s) on your answer sheets.

4.0pt

Reaction of 1 with DDQ gives highly conjugated compound H. Also, thermal reaction of coumpound H
with p-quinone gives I with molar mass of 226.28 g/mol.
1.3

Draw the structures of H, I, and J indicating stereochemistry.

6.0pt

Hints:• During the formation of I, sequential pericyclic reactions and an oxidation reaction (due to thepresence of O2 ) take place, and a well-known gas forms during the reaction.
• J has a strong and very broad band between 3300 and 2500 cm−1 in the IR spectrum.

Theory IChO 2020

A1-1
English (Oﬃcial)

Two Beauties of Turkey: the Van Cat and the Ankara Cat
1.1 (14.0 pt)

A

B

C

D

E

F

G

Theory IChO 2020

A1-2
English (Oﬃcial)

1.2 (4.0 pt)□ Enantiomers□ Diastereomers□ Identical□ Stereoisomers
1.3 (6.0 pt)

H

J

I

Theory IChO 2020

Q2-1
English (Oﬃcial)

A Tale of a Reactive Intermediate
Arynes constitute a special class of reactive intermediates. The ﬁrst experimental evidence for the structure of an aryne (benzyne) was demonstrated in 1953 via the elegant labeling experiments by John D.
Roberts and coworkers.
In one such experiment, chlorobenzene, whose carbon at position 1 was labeled with radioactive 14 C,
was reacted with KNH2 in liquid NH3 to give nearly equal amounts of isotopic isomers A and B along with
the inorganic salt C. This reaction proceeds via the formation of aryne intermediate D.

2.1

Draw the structures of A, B and D, and provide the formula of C. Indicate theposition(s) of 14 C-labeled carbon(s) with an asterisk (*) whenever applicable.

7.0pt

Analysis of the 14 C-labeled product(s) was achieved via degradation experiments (the 14 C-labeled carbons
are not shown on the structures). Radioactivities of the intermediates and ﬁnal products were examined.

Theory IChO 2020

Q2-2
English (Oﬃcial)

2.2

Tick the appropriate boxes on the answer sheet for the intermediates and products that you expect to exhibit radioactivity.

9.0pt

With the aim of facilitating aryne formation, Kobayashi and co-workers developed a ﬂuoride -induced
aryne generation protocol. Using this method, benzene derivative 3 is reacted with furan (4) in the presence of CsF, resulting in the formation of E, F, and G.

• Combustion analysis of E revealed the following atom content: 75.8% carbon, 5.8% hydrogen, and18.4% oxygen.
• E does not have a proton that is exchangeable with D2 O in 1 H-NMR spectroscopy.
• F is an ionic compound.
2.3

Determine the structures of E, F, and G (without stereochemical details).

8.0pt

In the absence of a nucleophile or a trapping agent, arynes can undergo [2+2]-type cyclodimerization or[2+2+2]-type cyclotrimerization reactions under suitable conditions. The aryne derivative that is obtained
when 3 is treated with one equivalent of CsF in MeCN can give, in principle, four different dimerizationand trimerization products (H–K).
• H has two planes of symmetry.
• I is expected to exhibit 21 signals in its 13 C-NMR spectrum.
• I and J both exhibit an m/z value of 318.1 in their mass spectra.
2.4

Determine the structures of H–K.

16pt

When 5 is reacted with 𝛽-ketoester 6 in the presence of 2 equivalents of CsF at 80 °C, L is obtained as the
major product. The 1 H-NMR and 13 C-NMR data for L, recorded in CDCl3 , are as follows:• 1 H-NMR: 𝛿 7.79 (dd, J = 7.6, 1.5 Hz, 1H), 7.47–7.33 (m, 2H), 7.25–7.20 (m, 1H), 3.91 (s, 2H), 3.66 (s, 3H),
2.56 (s, 3H) ppm.
• 13 C-NMR: 𝛿 201.3, 172.0, 137.1, 134.4, 132.8, 132.1, 130.1, 127.5, 51.9, 40.2, 28.8 ppm.

Theory IChO 2020

Q2-3
English (Oﬃcial)

2.5

Determine the structure of L.

5.0pt

2.6

In the reaction shown in task 2.5, which of the statement(s) in the answer sheet
describe(s) the function of CsF?
• The pK𝑎 values of HF and 𝛽-ketoester 6 in dimethyl sulfoxide (DMSO) areabout 15 and 14, respectively.

4.0pt

Diazapyrone derivative 8 was shown to be a useful reactant for the construction of a variety of cyclic
frameworks. Its preparation from phenylglyoxylic acid (7) and its use in two different reactions are described below.
• Q and T are gases under ambient conditions.
• O and P are constitutional isomers.
• Q does not have any signals in its IR spectrum.
• Heating 1 mol of R at 85 °C generates 1 mol of reactive intermediate S.
• Reaction of 8 with two equivalents of S gives U, Q, and T.

Note:equiv= equivalentcat= catalyst
2.7

Determine the structures of M–U.

28.0ptTheory IChO 2020

A2-1
English (Oﬃcial)

A Tale of a Reactive Intermediate
2.1 (7.0 pt)

A

B

C

D

2.2 (9.0 pt)

Considering only A:

□
□
□
□

Compound 1
BaCO3 (Batch 1)
Compound 2
BaCO3 (Batch 2)

Considering only B:

□
□
□
□

Compound 1
BaCO3 (Batch 1)
Compound 2
BaCO3 (Batch 2)

Theory IChO 2020

A2-2
English (Oﬃcial)

2.3 (8.0 pt)

E

F

G

2.4 (16.0 pt)

H

I

J

K

Theory IChO 2020

A2-3
English (Oﬃcial)

2.5 (5.0 pt)

L

2.6 (4.0 pt)

□
□
□
□

F– hydrolyzes the triﬂuoromethanesulfonate (O3 SCF3 ) group of 5.
F– attacks the –SiMe3 group of 5.
F– acts as a base to deprotonate of 6.
F– acts as a nucleophile and attacks the ester group of 6.

Theory IChO 2020

A2-4
English (Oﬃcial)

2.7 (28.0 pt)

M

N

O and P

Q

R

S

T

U

Theory IChO 2020

A2-1
English (Oﬃcial)

A Tale of a Reactive Intermediate
2.1 (7.0 pt)

A

B

C

D

2.2 (9.0 pt)

Considering only A:

□
□
□
□

Compound 1
BaCO3 (Batch 1)
Compound 2
BaCO3 (Batch 2)

Considering only B:

□
□
□
□

Compound 1
BaCO3 (Batch 1)
Compound 2
BaCO3 (Batch 2)

Theory IChO 2020

A2-2
English (Oﬃcial)

2.3 (8.0 pt)

E

F

G

2.4 (16.0 pt)

H

I

J

K

Theory IChO 2020

A2-3
English (Oﬃcial)

2.5 (5.0 pt)

L

2.6 (4.0 pt)

□
□
□
□

F– hydrolyzes the triﬂuoromethanesulfonate (O3 SCF3 ) group of 5.
F– attacks the –SiMe3 group of 5.
F– acts as a base to deprotonate of 6.
F– acts as a nucleophile and attacks the ester group of 6.

Theory IChO 2020

A2-4
English (Oﬃcial)

2.7 (28.0 pt)

M

N

O and P

Q

R

S

T

U

Theory IChO 2020

Q3-1
English (Oﬃcial)(±)-Coerulescine
A spiro compound is typically an organic compound containing rings linked together by one common
atom (spiroatom) as carbon atom with bold in ﬁgure below. The spiro[pyrrolidin-3,3′-oxindole] ring system is a structural framework incorporated in several cytostatic alkaloids and unnatural compounds.
Coerulescine (1) and horsﬁline are the simplest prototype members of this subfamily that show diverse
biological activity and can be synthesized by the route shown below.

Claisen rearrangement, which is a [3,3]-sigmatropic rearrangement, is a powerful carbon–carbon bondforming reaction in which an allyl vinyl ether is converted thermally to an unsaturated carbonyl compound as shown in the Scheme below. When compound A is heated, it undergoes Claisen rearrangement
to give carbonyl compound B.
For this entire task, your answers can be given without any stereochemical details.

Theory IChO 2020

Q3-2
English (Oﬃcial)

Theory IChO 2020

Q3-3
English (Oﬃcial)

3.1

Draw the structures of A and B.
• A is an inseparable mixture of cis/trans isomers.
• B has IR absorption at 1726 cm·φ .

8.0pt

3.2

Draw structures for C, D, E, and F.
• D–F have a bicyclic structure.

16.0pt3.3

Choose the correct order of steps for the transformation of F to G.

4.0pt

3.4

Draw structures for G and H (both spiro compounds).

8.0pt

3.5

Draw the structure of the intermediate produced by treatment with n-BuLi inthe step H → coerulescine (1).

5.0pt

Coerulescine (1), on treatment with N-bromosuccinimide (NBS), gives the bromo derivative, which uponheating with sodium methoxide in the presence of cuprous iodide gives horsﬁline (I) in 60% yield.
3.6

Choose the correct structure for compound I consistent with the following selected φ H-NMR data: δ 7.05 (d, J = 1.4 Hz, 1H), 6.78 (d, J = 8.0 Hz, 1H), 6.72 (dd, J= 8.0, 1.4 Hz, 1H) ppm.

5.0pt

3.7

When the allyl ether of 2 naphthol is heated a sigmatropic rearrangement isinitiated. Write the structure of major product isolated from this reaction.

5.0pt

Theory IChO 2020

A3-1
English (Oﬃcial)(±)-Coerulescine
3.1 (8.0 pt)

AB

3.2 (16.0 pt)

C

D

E

F

Theory IChO 2020

A3-2
English (Oﬃcial)

3.3 (4.0 pt)□□□

Imine formation, then reduction, then amidation
Amidation, then imine formation, then reduction
Reduction, then amidation, then imine formation

3.4 (8.0 pt)

G

3.5 (5.0 pt)

HTheory IChO 2020

A3-3
English (Oﬃcial)

3.6 (5.0 pt)

3.7 (5.0 pt)

Theory IChO 2020

Q4-1
English (Oﬃcial)

Symmetry Does Matter!
There are numerous reactions in organic chemistry that proceed through cyclic transition states andthese are classiﬁed as pericyclic reactions. Woodward–Hoffmann rules, developed by Robert B. Woodward and Roald Hoffmann, are used to rationalize stereochemical aspects and the activation energy of
pericyclic reactions.

Woodward–Hoffmann rules
Electrocyclic reactions

Cycloadditions

Number ofelectrons

Thermal (Δ)

Photochemical(ℎ𝜈)Thermal (Δ)

Photochemical(ℎ𝜈)

4n(n = 1, 2, ..)Conrotatory (con)Disrotatory

DisfavoredFavored

4n+2(n = 1, 2, ..)Disrotatory (dis)Conrotatory

FavoredDisfavored

4.1

Fill in the table for reactions (i)–(iii) or products 2–5:

12.0ptThere are three possible benzotropone isomers. Although two of the benzotropone isomers were isolated, 3,4-benzotropone (1) has not been isolated. Its instability is attributed to the o-quinoidal structureof 1 because it has no sextet electron system in the benzene ring.
4.2

Draw the structures of stable benzotropone isomers A (with 6 signals in its 13 CNMR) and B (with 11 signals in its 13 C-NMR).

6.0pt

Theory IChO 2020

Q4-2
English (Oﬃcial)

4.3

When the following tetraene is reacted under photochemical conditions,symmetry-allowed product(s) of three different ring sizes can form according
to the Woodward–Hoffmann rules. Tick the correct answer in each row.

6.0pt

The Nobel Prize in Chemistry 2015 was awarded jointly to the Turkish scientist Aziz Sancar, Swedish scientist Tomas Lindahl, and American scientist Paul Modrich for their “mechanistic studies of DNA repair”.
Pyrimidine bases found in DNA may undergo a photochemical [2+2]-cycloaddition reaction (see aboveﬁgure) with UV light that reaches a person’s skin, causing damage to DNA, which may ultimately lead toskin cancer. The research by Professor Aziz Sancar focused on the DNA repair mechanism for this typeof damage.
Thymine (T) is one of the nucleobases that can undergo such a photochemical reaction with UV light. Let
us assume that we have a solution of free thymine that was subjected to UV irradiation.

4.4

Considering stereochemistry, draw the structures of all possible products ofthis reaction between two free thymine (T) molecules. Circle the compound(s)which is/are chiral. Drawing only one enantiomer of an enantiomeric pair is
suﬃcient. Please note that only C=C bonds participate in this reaction.

16.0ptA broad range of halogenated derivatives of norbornadiene (N) are known in the literature. Tribromonorbornadiene (C7 H5 Br3 ) has six achiral isomers. Three of these isomers (6, 7, and 8) are given below.

Theory IChO 2020

Q4-3
English (Oﬃcial)

4.5

How many signals do you expect from the 13 C-NMR spectra of isomers 6, 7, and
8? Fill in the following boxes.

9.0pt

4.6

Draw structures of the remaining achiral tribromo-norbornadiene (C7 H5 Br3 )isomers (C, D, and E) in addition to 6–8 over the given ﬁgures in the boxes.

9.0pt

The NMR spectrum of ether 9 is complex. Two MeO– groups are different as are all the hydrogen atoms
on the rings. However, diphenol 10 has a very simple NMR spectrum and there are only three types ofprotons (marked as a, b, and c). A reasonable average structure responsible for all resonance structuresand its symmetry is shown as 11.

4.7

How many signals do you expect from the 13 C- and 1 H-NMR spectra of 12 and
13?

8.0pt

Theory IChO 2020

A4-1
English (Oﬃcial)

Symmetry Does Matter!
4.1 (12.0 pt)

Reaction

Product

i

2

ii

3

iii

[? + ?] cycloaddition

45

4.2 (6.0 pt)

AB

Δ or ℎ𝜈Theory IChO 2020

A4-2
English (Oﬃcial)

4.3 (6.0 pt)

4.4 (16.0 pt)

Theory IChO 2020

A4-3
English (Oﬃcial)

4.5 (9.0 pt)

6

7

8

C

D

E

4.6 (9.0 pt)

4.7 (8.0 pt)

1213..….. signals in 13 C-NMR..….. signals in 13 C-NMR……. signals in 1 H-NMR……. signals in 1 H-NMR

Theory IChO 2020

Q5-1
English (Oﬃcial)

Konya, Carrot, Beta-Carotene, Vitamin-A, Immune System, Vision

Mevlana (Rumi) was a great mystic and Suﬁ poet who lived out his days in Konya in the 13𝑡ℎ century. The
indirect relevance of Konya to chemistry is that the city provides 65% of the country’s carrot production,from which one of the essential vitamins (vitamin A) is obtained.
Carrot is an important source of β-carotene, which gives the vegetable its orange color. This molecule is a
red-orange pigment naturally found in plants and fruits and is a provitamin A carotenoid. It is converted
to vitamin A, which is essential for normal growth and development, the immune system, and visionfunction.
β-Carotene has an extended polyene chain of 22 carbon atoms. It is a conjugated π-system, having
alternating single and double bonds. Its experimental maximum absorption wavelength (𝜆𝑚𝑎𝑥 ) is 455
nm. We assume that all the bonds between C1 and C22 are conjugated bonds. There are 22 π-electrons
in the molecule (Figure 1).

Figure 1. Ball and stick representation of the structure of β-carotene. The gray and whitespheres represent the carbon and hydrogen atoms, respectively. The numbered carbon atoms
belong to the linear conjugated π-segment of the molecule.
To a crude approximation, the electrons in the C-2Pz orbitals, which are perpendicular to the molecularplane, are assumed to move along the entire molecule, without interacting with each other. They arelike independent particles conﬁned in a molecule moving along the x-axis in one dimension. These characteristics of π-electrons make them eligible for being treated by the simplest model called the particle
in one-dimensional box model.

Theory IChO 2020

Q5-2
English (Oﬃcial)

The wave function and the energies of the quantized levels for an electron moving in a one-dimensional
box with inﬁnite potential walls are given as follows:Ψ𝑛 (𝑥) = √ 𝐿2 sin 𝑛𝜋𝑥
𝐿(Eq.1)

where n is the quantum number, n=1,2,3,4,…. ∞, and L is the box length.
2(Eq.2)2𝑛 ℎ
𝐸𝑛 = 8𝑚
𝐿2𝑒

In two dimension, within the framework of independent particle approximation, the wavefunction isexpressed as a product of one-dimensional wavefunctions, and the energy is expressed as a sum of
one-dimensional energies. The energy levels of the two dimensional rectangular box is given as follows:
2

2

2

𝑥

𝑦

𝑒

𝑛𝑦
𝑛𝑥
ℎ
𝐸𝑛𝑥 ,𝑛𝑦 = [ 𝐿
2 + 𝐿 2 ]{ 8𝑚 }(Eq.3)

where n𝑥 , n𝑦 are the quantum numbers and they are positive integers. L𝑥 , L𝑦 are the dimensions of thebox in the 2D model. They are positive numbers.
5.1

Which two of the sentences given below are correct? Tick only one answer
which includes correct sentences in your answer sheet.

13.0ptThe β-carotene molecule is orange in color because:i) it absorbs in the visible region of the electromagnetic spectrum.
ii) HOMO →LUMO transition occurs by absorption of IR photon.
iii) the spacing between the 22𝑛𝑑 and the 23𝑟𝑑 energy levels is equal to the energy of the IR photon at
the orange wavelength.
iv) it absorbs green/blue light and it transmits red/yellow color.
v) it absorbs in the UV-Vis region since the molecule has no net dipole moment.
Although it is highly unrealistic, let us assume that the conjugated segment of the molecule is linear andtreated with the particle in a one-dimensional box model as shown in ﬁgure 2. In this case, the lengthof the box can be approximated as L=1.40×n𝐶 (in Å), where n𝐶 is the number of carbon atoms in the
conjugated segment.
Use this information to answer the questions 5.2–5.6.

Figure 2. Schematic representation of the conjugated line segment made up carbon atomsof β-carotene in a one-dimensional box of length L.

Theory IChO 2020

Q5-3
English (Oﬃcial)

5.2

Calculate the energies (in J) of the lowest two energy levels

13.0pt5.3

Draw the wavefunctions of the lowest two energy levels with proper labellingthe x-axis.

15.0pt5.4

Sketch the energy level diagram up to n = 4 showing the relative spacing.

8.0pt

5.5

What is the total 𝜋-energy (in J) of the molecule?

12.0pt5.6

Calculate the wavelength (in nm) at which the transition between the highest
occupied and lowest unoccupied energy levels occurs.

10.0pt

Use the particle in a two-dimensional box model to answer questions 5.7–5.8.

Figure 3. Schematic representation of the conjugated carbon atoms of β-carotene in a twodimensional box.
Assume that the conjugated segment is made up of carbon atoms that are all-trans to each other. The
motion of the 𝜋-electrons is studied in the two-dimensional rectangular box with the dimensions L𝑥 =26.0 Å, L𝑦 = 3.0 Å (Figure 3).
5.7

Calculate the energies (in J) of the highest occupied and the lowest unoccupied
energy levels and the wavelength (in nm) at which the transition between theseenergy levels occurs.

17.0pt5.8

What should be the L𝑥 value (in Å) in order for the molecule to absorb light at
the experimental λ𝑚𝑎𝑥 =455 nm if L𝑦 is kept constant at 3.0 Å. (Assume that thequantum numbers for homo and lumo are the same as in the question 5.7.)

12.0ptTheory IChO 2020

A5-1
English (Oﬃcial)

Konya, Carrot, Beta-Carotene, Vitamin-A, Immune System, Vision
5.1 (13.0 pt)□ a) i and ii□ e) ii and iii□ j) iii and v
5.2 (13.0 pt)

Calculation:

5.3 (15.0 pt)□ b) i and iii□ f) ii and iv□ k) iv and v□ c) i and iv□ g) ii and v□ d) i and v□ h) iii and iv

Theory IChO 2020

A5-2
English (Oﬃcial)

5.4 (8.0 pt)

5.5 (12.0 pt)

Theory IChO 2020

A5-3
English (Oﬃcial)

5.6 (10.0 pt)

calculation:

5.7 (17.0 pt)

calculation:

Theory IChO 2020

A5-4
English (Oﬃcial)

5.8 (12.0 pt)

Theory IChO 2020

Q6-1
English (Oﬃcial)

Thermodynamics through an Interstellar JourneyPart 1
In a hypothetical universe, an unknown amount of diborane participates in the following reaction:
B2 H6 (g) + 6 H2 O(l) → 2 H3 BO3 (s) + 6 H2 (g)Assume that in this hypothetical universe, H3 BO3 (s) obtained from this reaction was completely sublimed
at 300 K. The necessary energy for sublimation was obtained through work released by one cycle of an
ideal heat engine in which one mole of monoatomic perfect gas ﬂows through the cycle described in thepressure (p) – volume (V) diagram below:• A→B; isothermal reversible expansion receiving 250 J by heat transfer (q𝐻 ) at a temperature of 1000
K (T𝐻 ) from a hot source.
• B→D; reversible adiabatic expansion.
• D→C; isothermal reversible compression at a temperature of 300 K (T𝐶 ) releasing some amount ofheat (q𝐶 ) to a cold sink.
• C→A; reversible adiabatic compression.

After heat transfers, the remaining energy is released as work (w). Also, q𝐻 and q𝐶 are related to T𝐶 and
T𝐻 as follows:
|𝑞𝐻 |
= 𝑇𝑇𝐻
|𝑞𝐶 |
𝐶

The eﬃciency of the cycle can be found by work released by cycle (w) divided by heat absorbed by cycle(q𝐻 ).
You are provided with the change in enthalpies of the following reactions at 300 K.

Theory IChO 2020

Q6-2
English (Oﬃcial)(1) B2 H6 (g) + 6 Cl2 (g) → 2 BCl3 (g) + 6 HCl(g)Δ𝑟 H(1)= -1326 kJ mol−1(2) BCl3 (g) + 3 H2 O(l) → H3 BO3 (g) + 3 HCl(g)Δ𝑟 H(2)= -112.5 kJ mol−1(3) B2 H6 (g) + 6 H2 O(l) → 2 H3 BO3 (s) + 6 H2 (g)Δ𝑟 H(3)= -493.4 kJ mol−1(4) 12 H2 (g) + 12 Cl2 (g) → HCl(g)Δ𝑟 H(4)= -92.3 kJ mol−1

6.1

Calculate the molar enthalpy of sublimation (in kJ mol−1 ) for H3 BO3 at 300 K.

5.0pt

6.2

Calculate the Δ𝑟 U (internal energy) in terms of kJ mol−1 at 300 K for the reactions (2) and (4) given above (assume ideal gas behavior for each gaseous
species in each reaction).

12.0pt6.3

Calculate the amount of overall work produced by a heat engine (|w|) in termsof J and the amount of overall heat released to the cold sink (|q𝐶 |) in terms of
J.

6.0pt

6.4

Calculate the eﬃciency of the heat engine described above.

3.0pt

6.5

Calculate the entropy change (ΔS) for A→B and D→C processes in the heatengine in terms of J K−1 .

6.0pt

6.6

Calculate the Gibbs energy change (ΔG) in terms of J for A→B and D→C processes in the heat engine.

6.0pt

6.7

Calculate the ratio of pressure at point A to the pressure at point B in the cycle
cycle (standard pressure: 1 bar).

5.0pt

6.8

Calculate the amount of H2 (g) (in moles) produced according to the reaction
given at the beginning of the task for one cycle of the engine.

3.0pt

Part 2
Interstellar journeys can be done by using diborane as rocket fuel. Combustion of diborane is shown
below:B2 H6 (g)+ 3O2 (g) → B2 O3 (s) + 3H2 O (g)Combustion of diborane is experimented in a 100 L closed container at different temperatures and theequilibrium conditions were recorded.

Theory IChO 2020

Q6-3
English (Oﬃcial)

8930 K

9005 KB2 H6 (g)0.38 mol

0.49 mol

H2 O(g)0.20 mol

0.20 molPartial pressure of O2 (g) was stabilized to 1 bar and kept constant at all conditions. Assume that in thishypothetical universe; Δ𝑟 S° and Δ𝑟 H° are independent of temperature, the standard molar entropy (S°) of
B2 O3 (s) does not change with pressure, all the gas species behave as an ideal gas, and all species remainin the same phase, without any further decomposition before or after reaction, at all temperatures then:
6.9

Calculate K𝑝 (pressure based equilibrium constant) at 8930 K and 9005 K.

8.0pt

6.10

Calculate Δ𝑟 G° of the reaction in terms of kJ mol−1 at 8930 K and 9005 K. (If you
failed to ﬁnd K𝑝 , please use K𝑝 (8930 K) =2, K𝑝 (9005 K) = 0.5)

6.0pt

6.11

Calculate Δ𝑟 G° (in terms of kJ mol−1 ), Δ𝑟 H° (in terms of kJ mol−1 ), and Δ𝑟 S° ((interms of J mol−1 K−1 ) of the combustion reaction at 298 K. (If you failed to ﬁnd
K𝑝 , please use K𝑝 (8930 K) =2, K𝑝 (9005 K) = 0.5)

6.0pt

6.12

Tick the correct answer in the table by determining whether combustion reactions are favored or not at given T below under standard pressure (1 bar).

8.0pt

6.13

Calculate the Δ𝑓 H ( kJ mol–1 ) and S°( kJ mol–1 K–1 ) of H2 O(g) using the values
given in the table below. (Δ𝑓 H = enthalpy of formation, S° = standard entropy)(If you fail to ﬁnd Δ𝑟 H° and Δ𝑟 S° of the combustion, please use ΔH° = 1000 kJ
mol-1, ΔS°= 150 J K–1 mol–1 )6.0pt

Δ𝑓 H (298 K)

S° (298 K)

B2 H6 (g)–136.40 kJ mol

0.23 kJ mol–1 K–1

O2 (g)

0.00 kJ mol–1

0.16 kJ mol–1 K–1

B2 O3 (s)–1273 kJ mol–1

0.05 kJ mol–1 K–1

Theory IChO 2020

A6-1
English (Oﬃcial)

Thermodynamics through an Interstellar Journey
6.1 (5.0 pt)

Show your calculation:

6.2 (12.0 pt)

Show your calculation:

6.3 (6.0 pt)

Show your calculation:

Theory IChO 2020

A6-2
English (Oﬃcial)

6.4 (3.0 pt)

Show your calculation:

6.5 (6.0 pt)

Show your calculation:

6.6 (6.0 pt)

Show your calculation:

Theory IChO 2020

A6-3
English (Oﬃcial)

6.7 (5.0 pt)

Show your calculation:

6.8 (3.0 pt)

Show your calculation:

Theory IChO 2020

A6-4
English (Oﬃcial)

6.9 (8.0 pt)

Show your calculation:

Theory IChO 2020

A6-5
English (Oﬃcial)6.10 (6.0 pt)

Show your calculation:

6.11 (6.0 pt)

Show your calculation:

Theory IChO 2020

A6-6
English (Oﬃcial)6.12 (8.0 pt)

favored298 K8930 K
9005 K
9100 K
6.13 (6.0 pt)

Show your calculation:

□
□
□
□

Unfavored□□□□

Theory IChO 2020

Q7-1
English (Oﬃcial)

Phthalocyanines

The term phthalocyanine (Pc) takes its origin from the Greek “naphtha”, which means rock oil, and “cyanine”, which means dark blue. Turkish scientist Özer Bekaroğlu can be regarded as the pioneer of Pc
chemistry in Turkey.
Metal-free phthalocyanine (1, H2 Pc) is a large planar macrocyclic compound with the formula(C8 H4 N2 )4 H2 .
7.1

How many 𝜋-electrons are there in the bold region of the H2 Pc molecule in compound 1 shown above?

4.0pt

Theory IChO 2020

Q7-2
English (Oﬃcial)

Pcs containing one or two metal ions are called metallo-phthalocyanines (MPcs) and they exhibit different
geometries as given above.
7.2

Complete the table in your answer sheet by determining the coordination number of central ions in 2–5.

8.0pt

7.3

Complete the table in your answer sheet by determining the oxidation numberof each metal (Cu, Ti, and Ce) in 2, 3, and 5.

6.0pt

7.4

Complete the table in your answer sheet by determining the geometry of compounds 2–5.

8.0pt

7.5

Complete the table in your answer sheet by determining the magnetic property
of compounds 2–5.
• Use the letter "p" for paramagnetic property and letter "d" for a diamagnetic property.

8.0pt

7.6

Write the ground-state electron conﬁguration of the silicon (Si) ion in the compound 4, and ﬁnd all the quantum numbers for the 2p electrons in its groundstate.

14.0ptMetal-free phthalocyanine (1, H2 Pc) is commonly formed through the cyclotetramerization of phthalonitriles. On the other hand, Pcs having different substituents are called asymmetric, which can be preparedby the statistical cyclization of two different phthalonitriles. This method has no selectivity and the product is a mixture of all possible isomers.
7.7

Draw the possible products that may occur in the statistical cyclization methodby using F and G. If there are any stereoisomers label as cis- or trans-.
• F and G represent two different symmetrical phthalonitriles.
• One of the products is F4 as given below.
• Draw other products similar to the format in F4 .

19.0ptPcs are used as photosensitizers in the photodynamic therapy (PDT) of cancer due to their strong absorption in the visible spectrum and high molar absorption coeﬃcients. PDT consists of three essential

Theory IChO 2020

Q7-3
English (Oﬃcial)components: photosensitizer, light, and oxygen. None of these is individually toxic, but together they
initiate a photochemical reaction resulting in the generation of cytotoxic singlet oxygen (1 O2 ) that can
destroy cancer cells.
(multiplicity) 1 O2
• The multiplicity of an energy level is deﬁned as 2S+1
• If the two spins are parallel (↑↑), S = 1, and if the two spins are antiparallel (↑↓), S = 0.
7.8

Draw the molecule orbital (MO) diagram of the lowest energy singlet state ofdioxygen (1 O2 ) and calculate bond order.
• There are no unpaired electrons in that state!

12.0pt7.9

If the wavelength of the light needed to excite triplet oxygen into singlet oxygen is 1270 nm, calculate the energy (in kJ per mole) needed for this transition
process.

6.0pt

Theory IChO 2020

A7-1
English (Oﬃcial)

Phthalocyanines
7.1 (4.0 pt)

The number of 𝜋-electrons in an H2 Pc:

7.2 (8.0 pt)

Central ion

Copper ion

Titanium ion

Silicon ion

Cerium ion

Coordination number
7.3 (6.0 pt)

Metal in compounds

2

3

Oxidation number
7.4 (8.0 pt)

Geometry
Octahedral
Square prism
Square pyramidal
Square planar

Compound5

Theory IChO 2020

A7-2
English (Oﬃcial)

7.5 (8.0 pt)

CompoundMagnetic property

2345
7.6 (14.0 pt)

Electron conﬁguration:nQuantum numbers for 2p electrons:

l

m1

m𝑠

Theory IChO 2020

A7-3
English (Oﬃcial)

7.7 (19.0 pt)

Products:

Theory IChO 2020

A7-4
English (Oﬃcial)

7.8 (12.0 pt)

MO diagram:

Bond order:
7.9 (6.0 pt)

Show you calculation:

Energy = ……......………… kJ/mol

Theory IChO 2020

Q8-1
English (Oﬃcial)

Boron Compounds and Hydrogen Storage

Sodium borohydride (NaBH4 ) and ammonia borane (BNH6 ) are the most studied chemical hydrogen storage materials. In this question, you will explore the chemistry of boron and the use of boron compounds
as hydrogen storage materials.
Borax (Na2 B4 O7 ∙nH2 O) is a boron mineral that is produced by ETI Mining Company in Turkey. NaBH4 canbe synthesized by the reduction of anhydrous borax with metallic sodium under high-pressure hydrogengas in the presence of silicon dioxide (silica) at 700 °C, namely the Bayer process. In this process, allhydrogen is stored in NaBH4 . On the other hand, it has been shown that ammonia borane (BNH6 ) can besynthesized by the reaction of NaBH4 and ammonium sulfate in dry tetrahydrofuran (THF) at 40 °C (Hint:
BNH6 synthesis must be conducted in a well-ventilated fume-hood because ﬂammable gas is generated
as one of the by-products). While NaBH4 is an ionic compound, ammonia borane is a Lewis acid–baseadduct.
8.1

Write a balanced chemical equation for the synthesis of NaBH4 from anhydrous
borax.

3.0pt

8.2

Write a balanced chemical equation for the synthesis of ammonia borane from
NaBH4 .

3.0pt

8.3

Draw the molecular geometries of the BH−
4 ion and BNH6 molecule.

4.0pt

8.4

Calculate the hydrogen content of NaBH4 and BNH6 as a percentage by mass(wt%).

4.0pt

The hydrogen stored in both compounds can be released via hydrolysis reactions in the presence ofa suitable catalyst at room temperature. Upon the hydrolysis reactions, 4 and 3 moles of H2 gas are

Theory IChO 2020

Q8-2
English (Oﬃcial)released from the hydrolysis of 1 mole of NaBH4 and BNH6 , respectively, along with metaborate anion
including B-O bonds.
8.5

Write the balanced chemical equations for the hydrolysis of NaBH4 and BNH6 .

4.0pt

One of the simplest stable borates is diboron trioxide (B2 O3 ). Higher borates such as B3 O3−
6 having cyclic
structures containing B-O-bonds can be formed. Since B2 O3 is an acidic compound, it is easily reactedwith water to produce boric acid (H3 BO3 ). On the other hand, the high temperature and high-pressure
reaction of B2 O3 with ammonia yields two-dimensional boron nitride, which consists of planar graphitelike sheets of alternating B and N atoms.
8.6

Write the balanced chemical equations for the synthesis of boric acid and boron
nitride.

4.0pt

8.7

Draw the molecular structures of the B3 O3−
6 ion, boric acid, and a single twodimensional boron nitride sheet. Hint: show at least 10 B atoms in the boron
nitride structure.

6.0pt

Furthermore, B-H compounds, called boranes, are an important class of boron compounds. The simplest
stable borane is diborane (B2 H6 ) and many of the higher boranes can be prepared by the pyrolysis ofdiborane. Diborane can be synthesized via metathesis of a boron halide and a hydride source.
8.8

Write a balanced chemical equation for the synthesis of diborane from the reaction of BF3 and LiBH4 . Hint: both products are boron compounds.

3.0pt

8.9

Draw the molecular geometry of the diborane molecule. Hint: there is no B-B
bond in the molecule.

2.0pt

BH3 (borane) is an unstable and highly reactive molecule. Therefore, it is not possible to isolate it as BH3
under ordinary conditions. However, it can be stabilized via its reaction with carbon monoxide to yieldborane carbonyl (BH3 CO) compound, which is an adduct of borane. The preparation of BH3 CO plays animportant role in exploring the chemistry of boranes as it indicates the likely existence of the borane
molecule.
8.10

Sketch the Lewis dot structure of BH3 CO molecule by showing the formal
charges.

3.0pt

8.11

Which of the statements given in the answer sheet is observed in the C−O bondof a CO molecule upon the bond formation between BH3 and CO ? Tick thecorrect box.

2.0pt

Borazine consists of single and double bonded cyclic B−N units and hydrogen atoms attached to theseatoms with the molecular formula B3 N3 H6 and is isostructural to benzene. Borazine can be synthesized
by using a two-step procedure including the synthesis of symmetrically trisubstituted chlorine derivatives of borazine (B3 N3 H3 Cl3 ) from the reaction of ammonium chloride and boron trichloride, and thenreduction of B3 N3 H3 Cl3 with LiBH4 in THF.

Theory IChO 2020

Q8-3
English (Oﬃcial)

8.12

Write the balanced chemical equations for the two-step synthesis of borazine
starting from ammonium chloride in THF (tetrahydrofuran). Hint: THF stabilizes one of the products by forming a lewis acid-base adduct.

4.0pt

8.13

Draw the molecular structures of borazine and its symmetrically trisubstituted
chlorine derivative.

4.0pt

Catalysts are substances that accelerate the rate of reactions by allowing them to proceed in a lower
energy pathway. The catalytic activity of the catalysts is generally determined by the turnover frequency(TOF), which is calculated by dividing the molar amount of the product to the mole of active catalyst andthe time (TOF = mole product/(mole catalyst x time)). A typical hydrolysis of BNH6 was carried out in 10.0
mL of water by using 100.0 mM BNH6 and 5.0 mg of CuPt/C catalyst (CuPt alloy nanoparticles supported
on carbon black containing 8.2 wt% Pt atom).67.25 mL of hydrogen gas was generated in 5 minutes.
8.14

Assuming the catalytic reaction is performed in standard conditions (1atm and 273.15 K), calculate the TOF (min−1 ) of the CuPt/C catalyst
in terms of only Pt atoms in the hydrolysis of BNH6 by considering the volumeof the hydrogen gas generated.

4.0pt

As a result of detailed crystal analysis of a synthesized Cu𝑥 Pt𝑦 alloy nanoparticle (the subscripts indicate
molar percentages of the atoms in the alloy structure), it was determined that the face centered cubic(fcc) unit cell was formed by Pt atoms and the Pt atoms on the face of the fcc unit cell are supposed to be
replaced with Cu atoms to form Cu𝑥 Pt𝑦 displacement alloy nanoparticles. According to this information,
answer the following questions.
8.15

Determine the composition of the alloy nanoparticles by ﬁnding x and y in the
Cu𝑥 Pt𝑦 alloy composition.

2.0pt

8.16

Sketch the shape of the described crystal unit cell of Cu𝑥 Pt𝑦 alloy nanoparticles
by showing the placement of atoms on the unit cell.

2.0pt

8.17

Another alloy has a Cu2 Pt1 composition. Assume that this alloy also has an fcc
unit cell with an edge length of 380 pm, but the Cu and Pt atoms are randomly
distributed in the atomic positions. Calculate the density of this alloy in g/cm3 .

4.0pt

Theory IChO 2020

A8-1
English (Oﬃcial)

Boron Compounds and Hydrogen Storage
8.1 (3.0 pt)

8.2 (3.0 pt)

8.3 (4.0 pt)

8.4 (4.0 pt)

Theory IChO 2020

A8-2
English (Oﬃcial)

8.5 (4.0 pt)

8.6 (4.0 pt)

8.7 (6.0 pt)

B3 O3−
6

Boric acid

Boron nitride

Theory IChO 2020

A8-3
English (Oﬃcial)

8.8 (3.0 pt)

8.9 (2.0 pt)

8.10 (3.0 pt)

Theory IChO 2020

A8-4
English (Oﬃcial)8.11 (2.0 pt)

□
□
□
□

It gets longer because there will be 𝜋-back donation from BH3 to CO.
It gets longer because CO donates 𝜋-bonding electrons to BH3
No or slight change on it because CO donates its mainly non-bonding electrons to BH3
It gets shorter because CO donates 𝜋* anti-bonding electrons to BH3 .

8.12 (4.0 pt)

8.13 (4.0 pt)

8.14 (4.0 pt)

Theory IChO 2020

A8-5
English (Oﬃcial)8.15 (2.0 pt)

8.16 (2.0 pt)

8.17 (4.0 pt)

Theory IChO 2020

Q9-1
English (Oﬃcial)

Quantiﬁcation of Heavy Metal Ions
For the quantitative analysis of heavy metal ions in a factory’s wastewater pool, the following steps havebeen applied by an analyzer at 298 K:
Step 1) 10-mL samples of each were obtained from ﬁve different regions in a wastewater pool, mixed ina 100-mL beaker, and then stirred for 5 minutes using a magnetic stirrer.
Step 2) 10-mL of sample solution was taken from the 100-mL beaker and 142 mg of Na2 SO4 was added
while stirring, followed by transfer to a three-electrode cell as seen in Figure 1a. In this electrochemicalcell, Pt wire, Ag/AgCl (3 M KCl), and Pt foil served as the working, reference, and counter electrodes,
respectively.
Step 3) These electrodes were connected to a potentiostat and a constant potential of –0.50 V vs. Ag/AgClfor 14 minutes was applied as seen in Figure 1b (horizontal line). It is assumed that 14 min. is suﬃcient
to complete the expected electrochemical reactions.

Figure 1. a) Electrochemical cell design; 1) Working electrode (Pt wire), 2) reference electrode(Ag/AgCl, 3M KCl), 3) counter electrode (Pt foil), 4) cell tap, 5) electrochemical cell, 6) 10-mLof sample solution. b) Potential change of working electrode as a function of time. y-axis:
potential/V vs Ag/AgCl, x-axis: time/min.
Step 4) The electrodes were rinsed with distilled water, placed into another electrochemical cell including
10-mL of 0.1 M H2 SO4 solution, and potential was scanned between –0.50 and +0.50 V as seen in Figure
1b (downward sloping line in 2 min.). Current vs. potential data for this step are presented in Figure 2a,which is like an excellent view of Mount Ararat (Ağrı Dağı), the highest mountain in Turkey (Figure 2b).

Theory IChO 2020

Q9-2
English (Oﬃcial)

Figure 2. a) Potential scan of the working electrode as a function of current in 0.1 M H2 SO4
solution after keeping it constant at a potential of –0.50 V in 10-mL of wastewater sample asseen in Figure 1b (horizontal line). y-axis: current/𝜇A, x-axis: potential/V vs Ag/AgCl, b) A viewof Great and Little Ararat peaks.
Step 5) Another 10-mL of the sample solution prepared in step 1 was taken and the processes explainedin steps 2 and 3 were applied in that order. The electrodes were rinsed with distilled water and placed
into 10-mL of 0.1 M H2 SO4 solution. Then the potential of the working electrode was kept constant at+0.05 V for 14 min. It is assumed that 14 minutes is suﬃcient to complete the expected electrochemical
reactions.
Step 6) After step 5 was performed, the solution in the electrochemical cell was placed in a suitable ovento evaporate at 150 °C until dry solid was obtained.
Step 7) 5-mL of ethylenediaminetetraacetic acid (EDTA, H4 Y) (Figure 3) solution was added to the solid
obtained in step 6 and it was shaken to dissolve. It is known that 1-mL of EDTA solution is equivalent to3.85 mg/mL BaCO3 . Then, pH of the solution was adjusted to 10.0. Excess EDTA was titrated with standard 0.0010 M Ni(NO3 )2 solution and it was observed that 95.60 mL of Ni(NO3 )2 solution was consumed
up to the endpoint.

Theory IChO 2020

Q9-3
English (Oﬃcial)

Figure 3. Chemical structure of EDTA (H4 Y).
• In water saturated with H2 S, equilibrium concentration of [H2 S] is 0.1 M.
• K𝑠𝑝 (NiS) = 4.0 × 10–20 ; K𝑠𝑝 (CuS) = 1.0 × 10–36• K𝑎1 (H2 S) = 9.6 × 10–8 ; K𝑎2 (H2 S) = 1.3 × 10–14
Reaction

E˚/V (at 298 K)

2H2 O(l)+2e → H2 (g)+2OH (aq)

-0.83

Ni

(aq)+2𝑒 → Ni(s)

-0.24

−

2+

−

−

+

−

2H (aq)+2𝑒 → H2 (g)

0.00

2+

Cu

(aq)+2𝑒 → Cu(s)

+0.34

−

Ag+ (aq)+e− → Ag(s)+0.80

O2 (g)+4H (aq)+4e →2H2 O(l)

+1.23

+

−

9.1

Which of the following can be considered for peak 1 and peak 2 in Figure 2a,
respectively? Tick the correct box on the answer sheet.

5.0pt

9.2

Which of the statements is expected, if the potential is applied as –1.2 V insteadof –0.5 V at the ﬁrst step (horizontal line) in Figure 1b? Tick the correct box on
the answer sheet.

5.0pt

9.3

Calculate the scan rate of data presented in Figure 2a as mV/s at 298 K.

8.0pt

The potential of the following cell is measured as 0.437 V.
Pt,H2 (0.92 bar)|HCl(1.50×10−2 M),AgCl(sat)|Ag
9.4

Calculate the standard electrode potential value (V) of half-cell of AgCl(s)+e− →Ag(s)+Cl− (aq) at 298 K.
Note: You must show all works.

16.0pt9.5

Which of the statements is the main purpose of step 5 in this analysis? Tick thecorrect box on the answer sheet.

5.0pt

Theory IChO 2020

Q9-4
English (Oﬃcial)

9.6

Write net ionic equations for the complexation and the back titration reactionof step 7 on the answer sheet.

6.0pt

9.7

Calculate Ni2+ concentration as mg/L in the wastewater of the factory. Note:
You must show all works.

25.0pt9.8

Calculate the minimum pH value for starting the precipitation of Ni2+ ions inthe solution obtained in step 5 by passing saturated H2 S gas into the solution
until saturation. If you cannot solve question 9.7, use 20 mg/L Ni2+ sample forthis question. Note: You must show all works.

30.0ptTheory IChO 2020

A9-1
English (Oﬃcial)

Quantiﬁcation of Heavy Metal Ions
9.1 (5.0 pt)

□
□
□
□
□

Peak 1: electrochemical reduction of Ni / Peak 2: electrochemical reduction of Cu
Peak 1: electrochemical reduction of Cu / Peak 2: electrochemical reduction of Ni
Peak 1: electrochemical reduction of Ni / Peak 2: electrochemical oxidation of Cu
Peak 1: electrochemical oxidation of Ni / Peak 2: electrochemical oxidation of Cu
Peak 1: electrochemical oxidation of Cu / Peak 2: electrochemical oxidation of Ni

9.2 (5.0 pt)

□
□
□
□
□

NO evolution
NO2 evolution
Nitrogen evolution
Oxygen evolution
Hydrogen evolution

9.3 (8.0 pt)

Show your calculation:

Scan rate = ..................................................... mV/s

Theory IChO 2020

A9-2
English (Oﬃcial)

9.4 (16.0 pt)

Show your calculation:

Standard electrode potential =…………………… V
9.5 (5.0 pt)

□
□
□
□
□

Modiﬁcation of Pt wire with Ni–Cu alloy ﬁlm
Modiﬁcation of Pt wire with Ni ﬁlm
Electrochemical stripping of both Cu and Ni from Cu–Ni-modiﬁed Pt wire to the solution
Electrochemical stripping of Cu from Cu–Ni-modiﬁed Pt wire to the solution
Electrochemical stripping of Ni from Cu–Ni-modiﬁed Pt wire to the solution

9.6 (6.0 pt)

Complexation:

Back titration:

Theory IChO 2020

A9-3
English (Oﬃcial)

9.7 (25.0 pt)

Show your calculation:

Ni2+ concentration: …………............…………. mg/L:

Theory IChO 2020

A9-4
English (Oﬃcial)

9.8 (30.0 pt)

Show your calculation:

Minimum pH value: ………………………

Theory IChO 2020

G0-1
English (Oﬃcial)

General Instruction• Only write with pen. Your calculator should be non-programmable.
• This theoretical exam booklet contains 63 pages, not including general instructions.
• This examination has 9 problems.
• You will have 5 hours to solve the exam.
• Begin only when the START command is given.
• All results must be written in the appropriate boxes in pen in the designated areas on the answer
sheets. Use the back of the exam sheets if you need scratch paper. Remember that answers written
outside the answer boxes will not be graded.
• Write relevant calculations in the appropriate boxes when necessary. Full marks will be given forcorrect answers only when your work is shown.
• The invigilator will announce a 30-minute warning before the Stop command.
• You must stop working when the STOP command is given. Failure to stop writing will lead to thenulliﬁcation of your exam.
• The oﬃcial English version of this examination is available on request only for clariﬁcation.
• You are not allowed to leave your working place without permission. If you need any assistance(broken calculator, need to visit a restroom, etc), raise hand and wait until an invigilator arrives.
GOOD LUCK!

Theory IChO 2020

G0-2
English (Oﬃcial)

Problems & Grading Information

Problem
No

Title

Total
Score

% of Total Score

1

Two Beauties of Turkey: the Van Cat and the Ankara
Cat

24

8

2

A Tale of a Reactive Intermediate

77

10

3

(±)-Coerulescine

51

8

4

Symmetry Does Matter!

66

10

5

Konya, Carrot, Beta-Carotene, Vitamin-A, Immune
System, Vision

100

14

6

Thermodynamics through an Interstellar Journey

80

12

7

Phthalocyanines

85

12

8

Boron Compounds and Hydrogen Storage

58

14

9

Quantiﬁcation of Heavy Metal Ions

100

12

TOTAL

641

100

Theory IChO 2020

G0-3
English (Oﬃcial)

Authors
ALANYALIOĞLU, Murat, Atatürk UniversityAYDOĞAN, Abdullah, İstanbul Technical University
BURAT, Ayfer Kalkan, İstanbul Technical University
DAĞ, Ömer, Bilkent UniversityDAŞTAN, Arif, Atatürk UniversityKILIÇ, Hamdullah, Atatürk UniversityMETİN, Önder, Koç UniversitySARAÇOĞLU, Nurullah, Atatürk UniversityTÜRKMEN, Yunus Emre, Bilkent University
ÜNLÜ, Caner, İstanbul Technical University
YILMAZ, İsmail, İstanbul Technical University
YURTSEVER, Mine, İstanbul Technical University

EditorSARAÇOĞLU, Nurullah, Atatürk University

Theory IChO 2020

G0-4
English (Oﬃcial)

Physical Constants and Equations−1

Avogadro's number

𝑁𝐴 = 6.0221 × 1023 mol

Boltzmann constant𝑘𝐵 = 1.3807 × 10−23 JK−1

Universal gas constant𝑅 = 8.3145 JK−1 mol

Speed of light𝑐 = 2.9979 × 108 ms−1

Planck's constantℎ = 6.6261 × 10−34 Js

Faraday's constant𝐹 = 9.6485 × 104 C mol

Mass of electron

𝑚𝑒 = 9.1093 × 10−31 kg

Standard pressure

𝑃 = 1 bar = 105 Pa

Atmospheric pressure

𝑃𝑎𝑡𝑚 = 1.01325 × 105 Pa = 760 mmHg = 760 torr

Zero of the Celsius scale

273.15 K

1 picometer (pm)10−12 m; 1 Å = 10−10 m

1 nanometer (nm)10−9 m−1= 0.08205 atm LK−1 mol−1−1

1 eV = 1.6021 × 10−19 J
1 cal = 4.184 J
1 amu = 1.6605 × 10−27 kg
Charge of an electron

1.6021 × 10−19 C

Ideal gas equation

𝑃 𝑉 = 𝑛𝑅𝑇Theory IChO 2020

G0-5
English (Oﬃcial)

Physical Constants and Equations

Enthalpy

𝐻 = 𝑈 + 𝑃𝑉

Gibbs free energy

𝐺 = 𝐻 − 𝑇𝑆
Δ𝑟 𝐺 = Δ𝐺0 + 𝑅𝑇 𝑙𝑛𝑄0
Δ𝑟 𝐺0 = −𝑅𝑇 ln 𝐾 = −𝑛𝐹 𝐸𝑐𝑒𝑙𝑙

Entropy change

Δ𝑆 = 𝑞𝑟𝑒𝑣
𝑇 , where q𝑟𝑒𝑣 is heat for the reversible process

Entropy change

Δ𝑆 = 𝑛𝑅 ln 𝑣𝑣21 (for isothermal expansion of an ideal gas)

Nernst equation

𝐶𝑜𝑥𝑖𝑑𝑎𝑡𝑖𝑜𝑛
𝐸 = 𝐸 0 + 𝑅𝑇
𝑛𝐹 ln 𝐶

Energy of a photon

𝐸 = ℎ𝑐𝜆𝑟𝑒𝑑𝑢𝑐𝑡𝑖𝑜𝑛

Integrated rate law
Zeroth-orderFirst-order
Second order[𝐴] = [𝐴]0 − 𝑘𝑡ln [𝐴] = ln [𝐴]0 − 𝑘𝑡
1 = 1 + 𝑘𝑡
[𝐴]
[𝐴]0

Arrhenius equation𝑘 = 𝐴𝑒−𝐸𝑎 /𝑅𝑇

Equation of linear calibration curve𝑦 = 𝑚𝑥 + 𝑛

Lambert–Beer equation

𝐴 = 𝜀𝑙𝑐

Theory IChO 2020

G0-6
English (Oﬃcial)

Periodic Table of Elements

Theory IChO 2020

G0-7
English (Oﬃcial)

1

H-NMR Chemical Shifts

Typical Coupling Constants

geminal2
J = 0 Hz(homotopic hydrogens)vicinalJ = 2–12 Hz(depends on dihedral angle)
32

geminalJ = 0.5–3 Hz

geminalJ = 2–15 Hz(diastereotopic hydrogens)

3

2

3

cis
J = 7–12 Hz

allylic
J = 3–11 Hz(depends on dihedral angle)
3

3

vicinalJ = 6–8 Hz

trans
J = 12–18 Hz

J = 6–9 Hz (ortho)
J = 1–3 Hz (meta)
5
J = 0–1 Hz (para)

3

4

Theory IChO 2020

G0-8
English (Oﬃcial)

13

C-NMR Chemical Shifts

Theory IChO 2020

G0-9
English (Oﬃcial)

IR Absorption Frequency Table
Functional Group

Type of Vibration

Absorption Frequency
Region (cm–1 )Intensity(stretch, H-bonded)

3600–3200

strong, broad(stretch, free)3700–3500

strong, sharp(stretch)

1150–1050

strongstretch

3000–2850

strongbending1480–1350

variable

stretch3100–3010

mediumbending

1000–675

strongstretch1680–1620

variable

C–F

stretch1400–1000

strongC–Clstretch800–600

strongC–Br

stretch600–500

strong

C–I

stretch500

strongC–H

stretch3300

strong, sharp

C≡C

stretch2260–2100

variable, not present insymmetrical alkynes

Alcohol
O–H
C–O
AlkaneC–H
Alkene=C–H
C=C
Alkyl Halide

AlkyneTheory IChO 2020

G0-10
English (Oﬃcial)

IR Absorption Frequency Table
Amine
N–H

stretch3500–3300

medium(primaryamineshave
twobands;
secondaryamineshave
one
band, often very weak)

C–Nstretch1360–1080

medium-weakN–Hbending

1600

mediumC–H

stretch3100–3000

mediumC=C

stretch1600–1400

medium-weak, multiple bands

stretch1820–1670

strong

C=O

stretch1725–1700

strongO–H

stretch3300–2500

strong, very broad

C–O

stretch1320–1210

strong

C=O

stretch1740–1720

strongC–H

stretch2850–2820 & 2750–2720

medium, two peaks

stretch1690–1640

strongstretch3500–3100

unsubstituted
two bands

bending

1640–1550

Aromatic

Carbonyl
C=O
Acid

Aldehyde

Amide
C=O
N–H

have

Theory IChO 2020

G0-11
English (Oﬃcial)

IR Absorption Frequency Table
Anhydride
C=O

stretch1830–1800 & 1775–1740

two bands

C=O

stretch1750–1735

strongC–O

stretch1300–1000

two bands or morestretch1725–1705

strongstretch3-membered - 1850

strongstretch4-membered - 1780

strongstretch5-membered - 1745

strongstretch6-membered - 1715

strongstretch7-membered - 1705

strongstretch1685–1665

strong

Ester

Ketoneacyclic

cyclic𝛼, 𝛽-unsaturated

conjugation moves absorptions to lower wavenumbers
aryl ketone

stretch1700–1680

strongstretch1300–1000 (1150–1070)

strongstretch2260–2210

mediumstretch1560–1515 & 1385-1345

strong, two bands

Ether
C–O
Nitrile
C≡N
Nitro
N–O

Theory IChO 2020

Q1-1
English (Oﬃcial)

Two Beauties of Turkey: the Van Cat and the Ankara Cat

The most beautiful of cats, the Van cat is a pure breed living only in Lake Van basin. Another endemic cat
breed is the Ankara cat. They are called Angora cats. Their most important feature is their two different
eye colors.

Just like people, cats can sometimes be stressed and angry. Just as people are made happy by melatonin,
the stress of cats can be reduced and they can be made happy thanks to a natural product. Nepetalactone
is an organic compound isolated from the plant catnip (Nepeta cataria), which acts as a cat attractant.
Nepetalactone is a ten-carbon bicyclic monoterpenoid compound derived from isoprene with two fusedrings: a cyclopentane and a lactone.

Theory IChO 2020

Q1-2
English (Oﬃcial)

Total synthesis of nepetalactone:

1.1

The above scheme describes the total synthesis
Draw structures of A–G, without stereochemical details.

ofnepetalactone.

Hints:• Compound A has strong and sharp band at 3300 cm−1 in the IR spectrum.
• A, B, and F are monocyclic, while C, D, E, and G are bicyclic compounds.
• F has one doublet at ∼ 9.8 ppm in the 1 H-NMR spectrum.

14.0ptTheory IChO 2020

Q1-3
English (Oﬃcial)

Reactions of nepetalactone:

The above scheme includes a few reactions of one of the enantiopure nepetalactone 1 isomers. Threeof the reaction products (5, 6, and J) are used as insect repellents in industry.
1.2

For the relationship between 5 and 6, which of the following is/are true? Tickthe box next to the correct answer(s) on your answer sheets.

4.0pt

Reaction of 1 with DDQ gives highly conjugated compound H. Also, thermal reaction of coumpound H
with p-quinone gives I with molar mass of 226.28 g/mol.
1.3

Draw the structures of H, I, and J indicating stereochemistry.

6.0pt

Hints:• During the formation of I, sequential pericyclic reactions and an oxidation reaction (due to thepresence of O2 ) take place, and a well-known gas forms during the reaction.
• J has a strong and very broad band between 3300 and 2500 cm−1 in the IR spectrum.

Theory IChO 2020

A1-1
English (Oﬃcial)

Two Beauties of Turkey: the Van Cat and the Ankara Cat
1.1 (14.0 pt)

A

B

C

D

E

F

G

Theory IChO 2020

A1-2
English (Oﬃcial)

1.2 (4.0 pt)□ Enantiomers□ Diastereomers□ Identical□ Stereoisomers
1.3 (6.0 pt)

H

J

I

Theory IChO 2020

Q2-1
English (Oﬃcial)

A Tale of a Reactive Intermediate
Arynes constitute a special class of reactive intermediates. The ﬁrst experimental evidence for the structure of an aryne (benzyne) was demonstrated in 1953 via the elegant labeling experiments by John D.
Roberts and coworkers.
In one such experiment, chlorobenzene, whose carbon at position 1 was labeled with radioactive 14 C,
was reacted with KNH2 in liquid NH3 to give nearly equal amounts of isotopic isomers A and B along with
the inorganic salt C. This reaction proceeds via the formation of aryne intermediate D.

2.1

Draw the structures of A, B and D, and provide the formula of C. Indicate theposition(s) of 14 C-labeled carbon(s) with an asterisk (*) whenever applicable.

7.0pt

Analysis of the 14 C-labeled product(s) was achieved via degradation experiments (the 14 C-labeled carbons
are not shown on the structures). Radioactivities of the intermediates and ﬁnal products were examined.

Theory IChO 2020

Q2-2
English (Oﬃcial)

2.2

Tick the appropriate boxes on the answer sheet for the intermediates and products that you expect to exhibit radioactivity.

9.0pt

With the aim of facilitating aryne formation, Kobayashi and co-workers developed a ﬂuoride -induced
aryne generation protocol. Using this method, benzene derivative 3 is reacted with furan (4) in the presence of CsF, resulting in the formation of E, F, and G.

• Combustion analysis of E revealed the following atom content: 75.8% carbon, 5.8% hydrogen, and18.4% oxygen.
• E does not have a proton that is exchangeable with D2 O in 1 H-NMR spectroscopy.
• F is an ionic compound.
2.3

Determine the structures of E, F, and G (without stereochemical details).

8.0pt

In the absence of a nucleophile or a trapping agent, arynes can undergo [2+2]-type cyclodimerization or[2+2+2]-type cyclotrimerization reactions under suitable conditions. The aryne derivative that is obtained
when 3 is treated with one equivalent of CsF in MeCN can give, in principle, four different dimerizationand trimerization products (H–K).
• H has two planes of symmetry.
• I is expected to exhibit 21 signals in its 13 C-NMR spectrum.
• I and J both exhibit an m/z value of 318.1 in their mass spectra.
2.4

Determine the structures of H–K.

16pt

When 5 is reacted with 𝛽-ketoester 6 in the presence of 2 equivalents of CsF at 80 °C, L is obtained as the
major product. The 1 H-NMR and 13 C-NMR data for L, recorded in CDCl3 , are as follows:• 1 H-NMR: 𝛿 7.79 (dd, J = 7.6, 1.5 Hz, 1H), 7.47–7.33 (m, 2H), 7.25–7.20 (m, 1H), 3.91 (s, 2H), 3.66 (s, 3H),
2.56 (s, 3H) ppm.
• 13 C-NMR: 𝛿 201.3, 172.0, 137.1, 134.4, 132.8, 132.1, 130.1, 127.5, 51.9, 40.2, 28.8 ppm.

Theory IChO 2020

Q2-3
English (Oﬃcial)

2.5

Determine the structure of L.

5.0pt

2.6

In the reaction shown in task 2.5, which of the statement(s) in the answer sheet
describe(s) the function of CsF?
• The pK𝑎 values of HF and 𝛽-ketoester 6 in dimethyl sulfoxide (DMSO) areabout 15 and 14, respectively.

4.0pt

Diazapyrone derivative 8 was shown to be a useful reactant for the construction of a variety of cyclic
frameworks. Its preparation from phenylglyoxylic acid (7) and its use in two different reactions are described below.
• Q and T are gases under ambient conditions.
• O and P are constitutional isomers.
• Q does not have any signals in its IR spectrum.
• Heating 1 mol of R at 85 °C generates 1 mol of reactive intermediate S.
• Reaction of 8 with two equivalents of S gives U, Q, and T.

Note:equiv= equivalentcat= catalyst
2.7

Determine the structures of M–U.

28.0ptTheory IChO 2020

Q3-1
English (Oﬃcial)(±)-Coerulescine
A spiro compound is typically an organic compound containing rings linked together by one common
atom (spiroatom) as carbon atom with bold in ﬁgure below. The spiro[pyrrolidin-3,3′-oxindole] ring system is a structural framework incorporated in several cytostatic alkaloids and unnatural compounds.
Coerulescine (1) and horsﬁline are the simplest prototype members of this subfamily that show diverse
biological activity and can be synthesized by the route shown below.

Claisen rearrangement, which is a [3,3]-sigmatropic rearrangement, is a powerful carbon–carbon bondforming reaction in which an allyl vinyl ether is converted thermally to an unsaturated carbonyl compound as shown in the Scheme below. When compound A is heated, it undergoes Claisen rearrangement
to give carbonyl compound B.
For this entire task, your answers can be given without any stereochemical details.

Theory IChO 2020

Q3-2
English (Oﬃcial)

Theory IChO 2020

Q3-3
English (Oﬃcial)

3.1

Draw the structures of A and B.
• A is an inseparable mixture of cis/trans isomers.
• B has IR absorption at 1726 cm·φ .

8.0pt

3.2

Draw structures for C, D, E, and F.
• D–F have a bicyclic structure.

16.0pt3.3

Choose the correct order of steps for the transformation of F to G.

4.0pt

3.4

Draw structures for G and H (both spiro compounds).

8.0pt

3.5

Draw the structure of the intermediate produced by treatment with n-BuLi inthe step H → coerulescine (1).

5.0pt

Coerulescine (1), on treatment with N-bromosuccinimide (NBS), gives the bromo derivative, which uponheating with sodium methoxide in the presence of cuprous iodide gives horsﬁline (I) in 60% yield.
3.6

Choose the correct structure for compound I consistent with the following selected φ H-NMR data: δ 7.05 (d, J = 1.4 Hz, 1H), 6.78 (d, J = 8.0 Hz, 1H), 6.72 (dd, J= 8.0, 1.4 Hz, 1H) ppm.

5.0pt

3.7

When the allyl ether of 2 naphthol is heated a sigmatropic rearrangement isinitiated. Write the structure of major product isolated from this reaction.

5.0pt

Theory IChO 2020

A3-1
English (Oﬃcial)(±)-Coerulescine
3.1 (8.0 pt)

AB

3.2 (16.0 pt)

C

D

E

F

Theory IChO 2020

A3-2
English (Oﬃcial)

3.3 (4.0 pt)□□□

Imine formation, then reduction, then amidation
Amidation, then imine formation, then reduction
Reduction, then amidation, then imine formation

3.4 (8.0 pt)

G

3.5 (5.0 pt)

HTheory IChO 2020

A3-3
English (Oﬃcial)

3.6 (5.0 pt)

3.7 (5.0 pt)

Theory IChO 2020

Q4-1
English (Oﬃcial)

Symmetry Does Matter!
There are numerous reactions in organic chemistry that proceed through cyclic transition states andthese are classiﬁed as pericyclic reactions. Woodward–Hoffmann rules, developed by Robert B. Woodward and Roald Hoffmann, are used to rationalize stereochemical aspects and the activation energy of
pericyclic reactions.

Woodward–Hoffmann rules
Electrocyclic reactions

Cycloadditions

Number ofelectrons

Thermal (Δ)

Photochemical(ℎ𝜈)Thermal (Δ)

Photochemical(ℎ𝜈)

4n(n = 1, 2, ..)Conrotatory (con)Disrotatory

DisfavoredFavored

4n+2(n = 1, 2, ..)Disrotatory (dis)Conrotatory

FavoredDisfavored

4.1

Fill in the table for reactions (i)–(iii) or products 2–5:

12.0ptThere are three possible benzotropone isomers. Although two of the benzotropone isomers were isolated, 3,4-benzotropone (1) has not been isolated. Its instability is attributed to the o-quinoidal structureof 1 because it has no sextet electron system in the benzene ring.
4.2

Draw the structures of stable benzotropone isomers A (with 6 signals in its 13 CNMR) and B (with 11 signals in its 13 C-NMR).

6.0pt

Theory IChO 2020

Q4-2
English (Oﬃcial)

4.3

When the following tetraene is reacted under photochemical conditions,symmetry-allowed product(s) of three different ring sizes can form according
to the Woodward–Hoffmann rules. Tick the correct answer in each row.

6.0pt

The Nobel Prize in Chemistry 2015 was awarded jointly to the Turkish scientist Aziz Sancar, Swedish scientist Tomas Lindahl, and American scientist Paul Modrich for their “mechanistic studies of DNA repair”.
Pyrimidine bases found in DNA may undergo a photochemical [2+2]-cycloaddition reaction (see aboveﬁgure) with UV light that reaches a person’s skin, causing damage to DNA, which may ultimately lead toskin cancer. The research by Professor Aziz Sancar focused on the DNA repair mechanism for this typeof damage.
Thymine (T) is one of the nucleobases that can undergo such a photochemical reaction with UV light. Let
us assume that we have a solution of free thymine that was subjected to UV irradiation.

4.4

Considering stereochemistry, draw the structures of all possible products ofthis reaction between two free thymine (T) molecules. Circle the compound(s)which is/are chiral. Drawing only one enantiomer of an enantiomeric pair is
suﬃcient. Please note that only C=C bonds participate in this reaction.

16.0ptA broad range of halogenated derivatives of norbornadiene (N) are known in the literature. Tribromonorbornadiene (C7 H5 Br3 ) has six achiral isomers. Three of these isomers (6, 7, and 8) are given below.

Theory IChO 2020

Q4-3
English (Oﬃcial)

4.5

How many signals do you expect from the 13 C-NMR spectra of isomers 6, 7, and
8? Fill in the following boxes.

9.0pt

4.6

Draw structures of the remaining achiral tribromo-norbornadiene (C7 H5 Br3 )isomers (C, D, and E) in addition to 6–8 over the given ﬁgures in the boxes.

9.0pt

The NMR spectrum of ether 9 is complex. Two MeO– groups are different as are all the hydrogen atoms
on the rings. However, diphenol 10 has a very simple NMR spectrum and there are only three types ofprotons (marked as a, b, and c). A reasonable average structure responsible for all resonance structuresand its symmetry is shown as 11.

4.7

How many signals do you expect from the 13 C- and 1 H-NMR spectra of 12 and
13?

8.0pt

Theory IChO 2020

A4-1
English (Oﬃcial)

Symmetry Does Matter!
4.1 (12.0 pt)

Reaction

Product

i

2

ii

3

iii

[? + ?] cycloaddition

45

4.2 (6.0 pt)

AB

Δ or ℎ𝜈Theory IChO 2020

A4-2
English (Oﬃcial)

4.3 (6.0 pt)

4.4 (16.0 pt)

Theory IChO 2020

A4-3
English (Oﬃcial)

4.5 (9.0 pt)

6

7

8

C

D

E

4.6 (9.0 pt)

4.7 (8.0 pt)

1213..….. signals in 13 C-NMR..….. signals in 13 C-NMR……. signals in 1 H-NMR……. signals in 1 H-NMR

Theory IChO 2020

Q5-1
English (Oﬃcial)

Konya, Carrot, Beta-Carotene, Vitamin-A, Immune System, Vision

Mevlana (Rumi) was a great mystic and Suﬁ poet who lived out his days in Konya in the 13𝑡ℎ century. The
indirect relevance of Konya to chemistry is that the city provides 65% of the country’s carrot production,from which one of the essential vitamins (vitamin A) is obtained.
Carrot is an important source of β-carotene, which gives the vegetable its orange color. This molecule is a
red-orange pigment naturally found in plants and fruits and is a provitamin A carotenoid. It is converted
to vitamin A, which is essential for normal growth and development, the immune system, and visionfunction.
β-Carotene has an extended polyene chain of 22 carbon atoms. It is a conjugated π-system, having
alternating single and double bonds. Its experimental maximum absorption wavelength (𝜆𝑚𝑎𝑥 ) is 455
nm. We assume that all the bonds between C1 and C22 are conjugated bonds. There are 22 π-electrons
in the molecule (Figure 1).

Figure 1. Ball and stick representation of the structure of β-carotene. The gray and whitespheres represent the carbon and hydrogen atoms, respectively. The numbered carbon atoms
belong to the linear conjugated π-segment of the molecule.
To a crude approximation, the electrons in the C-2Pz orbitals, which are perpendicular to the molecularplane, are assumed to move along the entire molecule, without interacting with each other. They arelike independent particles conﬁned in a molecule moving along the x-axis in one dimension. These characteristics of π-electrons make them eligible for being treated by the simplest model called the particle
in one-dimensional box model.

Theory IChO 2020

Q5-2
English (Oﬃcial)

The wave function and the energies of the quantized levels for an electron moving in a one-dimensional
box with inﬁnite potential walls are given as follows:Ψ𝑛 (𝑥) = √ 𝐿2 sin 𝑛𝜋𝑥
𝐿(Eq.1)

where n is the quantum number, n=1,2,3,4,…. ∞, and L is the box length.
2(Eq.2)2𝑛 ℎ
𝐸𝑛 = 8𝑚
𝐿2𝑒

In two dimension, within the framework of independent particle approximation, the wavefunction isexpressed as a product of one-dimensional wavefunctions, and the energy is expressed as a sum of
one-dimensional energies. The energy levels of the two dimensional rectangular box is given as follows:
2

2

2

𝑥

𝑦

𝑒

𝑛𝑦
𝑛𝑥
ℎ
𝐸𝑛𝑥 ,𝑛𝑦 = [ 𝐿
2 + 𝐿 2 ]{ 8𝑚 }(Eq.3)

where n𝑥 , n𝑦 are the quantum numbers and they are positive integers. L𝑥 , L𝑦 are the dimensions of thebox in the 2D model. They are positive numbers.
5.1

Which two of the sentences given below are correct? Tick only one answer
which includes correct sentences in your answer sheet.

13.0ptThe β-carotene molecule is orange in color because:i) it absorbs in the visible region of the electromagnetic spectrum.
ii) HOMO →LUMO transition occurs by absorption of IR photon.
iii) the spacing between the 22𝑛𝑑 and the 23𝑟𝑑 energy levels is equal to the energy of the IR photon at
the orange wavelength.
iv) it absorbs green/blue light and it transmits red/yellow color.
v) it absorbs in the UV-Vis region since the molecule has no net dipole moment.
Although it is highly unrealistic, let us assume that the conjugated segment of the molecule is linear andtreated with the particle in a one-dimensional box model as shown in ﬁgure 2. In this case, the lengthof the box can be approximated as L=1.40×n𝐶 (in Å), where n𝐶 is the number of carbon atoms in the
conjugated segment.
Use this information to answer the questions 5.2–5.6.

Figure 2. Schematic representation of the conjugated line segment made up carbon atomsof β-carotene in a one-dimensional box of length L.

Theory IChO 2020

Q5-3
English (Oﬃcial)

5.2

Calculate the energies (in J) of the lowest two energy levels

13.0pt5.3

Draw the wavefunctions of the lowest two energy levels with proper labellingthe x-axis.

15.0pt5.4

Sketch the energy level diagram up to n = 4 showing the relative spacing.

8.0pt

5.5

What is the total 𝜋-energy (in J) of the molecule?

12.0pt5.6

Calculate the wavelength (in nm) at which the transition between the highest
occupied and lowest unoccupied energy levels occurs.

10.0pt

Use the particle in a two-dimensional box model to answer questions 5.7–5.8.

Figure 3. Schematic representation of the conjugated carbon atoms of β-carotene in a twodimensional box.
Assume that the conjugated segment is made up of carbon atoms that are all-trans to each other. The
motion of the 𝜋-electrons is studied in the two-dimensional rectangular box with the dimensions L𝑥 =26.0 Å, L𝑦 = 3.0 Å (Figure 3).
5.7

Calculate the energies (in J) of the highest occupied and the lowest unoccupied
energy levels and the wavelength (in nm) at which the transition between theseenergy levels occurs.

17.0pt5.8

What should be the L𝑥 value (in Å) in order for the molecule to absorb light at
the experimental λ𝑚𝑎𝑥 =455 nm if L𝑦 is kept constant at 3.0 Å. (Assume that thequantum numbers for homo and lumo are the same as in the question 5.7.)

12.0ptTheory IChO 2020

A5-1
English (Oﬃcial)

Konya, Carrot, Beta-Carotene, Vitamin-A, Immune System, Vision
5.1 (13.0 pt)□ a) i and ii□ e) ii and iii□ j) iii and v
5.2 (13.0 pt)

Calculation:

5.3 (15.0 pt)□ b) i and iii□ f) ii and iv□ k) iv and v□ c) i and iv□ g) ii and v□ d) i and v□ h) iii and iv

Theory IChO 2020

A5-2
English (Oﬃcial)

5.4 (8.0 pt)

5.5 (12.0 pt)

Theory IChO 2020

A5-3
English (Oﬃcial)

5.6 (10.0 pt)

calculation:

5.7 (17.0 pt)

calculation:

Theory IChO 2020

A5-4
English (Oﬃcial)

5.8 (12.0 pt)

Theory IChO 2020

Q6-1
English (Oﬃcial)

Thermodynamics through an Interstellar JourneyPart 1
In a hypothetical universe, an unknown amount of diborane participates in the following reaction:
B2 H6 (g) + 6 H2 O(l) → 2 H3 BO3 (s) + 6 H2 (g)Assume that in this hypothetical universe, H3 BO3 (s) obtained from this reaction was completely sublimed
at 300 K. The necessary energy for sublimation was obtained through work released by one cycle of an
ideal heat engine in which one mole of monoatomic perfect gas ﬂows through the cycle described in thepressure (p) – volume (V) diagram below:• A→B; isothermal reversible expansion receiving 250 J by heat transfer (q𝐻 ) at a temperature of 1000
K (T𝐻 ) from a hot source.
• B→D; reversible adiabatic expansion.
• D→C; isothermal reversible compression at a temperature of 300 K (T𝐶 ) releasing some amount ofheat (q𝐶 ) to a cold sink.
• C→A; reversible adiabatic compression.

After heat transfers, the remaining energy is released as work (w). Also, q𝐻 and q𝐶 are related to T𝐶 and
T𝐻 as follows:
|𝑞𝐻 |
= 𝑇𝑇𝐻
|𝑞𝐶 |
𝐶

The eﬃciency of the cycle can be found by work released by cycle (w) divided by heat absorbed by cycle(q𝐻 ).
You are provided with the change in enthalpies of the following reactions at 300 K.

Theory IChO 2020

Q6-2
English (Oﬃcial)(1) B2 H6 (g) + 6 Cl2 (g) → 2 BCl3 (g) + 6 HCl(g)Δ𝑟 H(1)= -1326 kJ mol−1(2) BCl3 (g) + 3 H2 O(l) → H3 BO3 (g) + 3 HCl(g)Δ𝑟 H(2)= -112.5 kJ mol−1(3) B2 H6 (g) + 6 H2 O(l) → 2 H3 BO3 (s) + 6 H2 (g)Δ𝑟 H(3)= -493.4 kJ mol−1(4) 12 H2 (g) + 12 Cl2 (g) → HCl(g)Δ𝑟 H(4)= -92.3 kJ mol−1

6.1

Calculate the molar enthalpy of sublimation (in kJ mol−1 ) for H3 BO3 at 300 K.

5.0pt

6.2

Calculate the Δ𝑟 U (internal energy) in terms of kJ mol−1 at 300 K for the reactions (2) and (4) given above (assume ideal gas behavior for each gaseous
species in each reaction).

12.0pt6.3

Calculate the amount of overall work produced by a heat engine (|w|) in termsof J and the amount of overall heat released to the cold sink (|q𝐶 |) in terms of
J.

6.0pt

6.4

Calculate the eﬃciency of the heat engine described above.

3.0pt

6.5

Calculate the entropy change (ΔS) for A→B and D→C processes in the heatengine in terms of J K−1 .

6.0pt

6.6

Calculate the Gibbs energy change (ΔG) in terms of J for A→B and D→C processes in the heat engine.

6.0pt

6.7

Calculate the ratio of pressure at point A to the pressure at point B in the cycle
cycle (standard pressure: 1 bar).

5.0pt

6.8

Calculate the amount of H2 (g) (in moles) produced according to the reaction
given at the beginning of the task for one cycle of the engine.

3.0pt

Part 2
Interstellar journeys can be done by using diborane as rocket fuel. Combustion of diborane is shown
below:B2 H6 (g)+ 3O2 (g) → B2 O3 (s) + 3H2 O (g)Combustion of diborane is experimented in a 100 L closed container at different temperatures and theequilibrium conditions were recorded.

Theory IChO 2020

Q6-3
English (Oﬃcial)

8930 K

9005 KB2 H6 (g)0.38 mol

0.49 mol

H2 O(g)0.20 mol

0.20 molPartial pressure of O2 (g) was stabilized to 1 bar and kept constant at all conditions. Assume that in thishypothetical universe; Δ𝑟 S° and Δ𝑟 H° are independent of temperature, the standard molar entropy (S°) of
B2 O3 (s) does not change with pressure, all the gas species behave as an ideal gas, and all species remainin the same phase, without any further decomposition before or after reaction, at all temperatures then:
6.9

Calculate K𝑝 (pressure based equilibrium constant) at 8930 K and 9005 K.

8.0pt

6.10

Calculate Δ𝑟 G° of the reaction in terms of kJ mol−1 at 8930 K and 9005 K. (If you
failed to ﬁnd K𝑝 , please use K𝑝 (8930 K) =2, K𝑝 (9005 K) = 0.5)

6.0pt

6.11

Calculate Δ𝑟 G° (in terms of kJ mol−1 ), Δ𝑟 H° (in terms of kJ mol−1 ), and Δ𝑟 S° ((interms of J mol−1 K−1 ) of the combustion reaction at 298 K. (If you failed to ﬁnd
K𝑝 , please use K𝑝 (8930 K) =2, K𝑝 (9005 K) = 0.5)

6.0pt

6.12

Tick the correct answer in the table by determining whether combustion reactions are favored or not at given T below under standard pressure (1 bar).

8.0pt

6.13

Calculate the Δ𝑓 H ( kJ mol–1 ) and S°( kJ mol–1 K–1 ) of H2 O(g) using the values
given in the table below. (Δ𝑓 H = enthalpy of formation, S° = standard entropy)(If you fail to ﬁnd Δ𝑟 H° and Δ𝑟 S° of the combustion, please use ΔH° = 1000 kJ
mol-1, ΔS°= 150 J K–1 mol–1 )6.0pt

Δ𝑓 H (298 K)

S° (298 K)

B2 H6 (g)–136.40 kJ mol

0.23 kJ mol–1 K–1

O2 (g)

0.00 kJ mol–1

0.16 kJ mol–1 K–1

B2 O3 (s)–1273 kJ mol–1

0.05 kJ mol–1 K–1

Theory IChO 2020

A6-1
English (Oﬃcial)

Thermodynamics through an Interstellar Journey
6.1 (5.0 pt)

Show your calculation:

6.2 (12.0 pt)

Show your calculation:

6.3 (6.0 pt)

Show your calculation:

Theory IChO 2020

A6-2
English (Oﬃcial)

6.4 (3.0 pt)

Show your calculation:

6.5 (6.0 pt)

Show your calculation:

6.6 (6.0 pt)

Show your calculation:

Theory IChO 2020

A6-3
English (Oﬃcial)

6.7 (5.0 pt)

Show your calculation:

6.8 (3.0 pt)

Show your calculation:

Theory IChO 2020

A6-4
English (Oﬃcial)

6.9 (8.0 pt)

Show your calculation:

Theory IChO 2020

A6-5
English (Oﬃcial)6.10 (6.0 pt)

Show your calculation:

6.11 (6.0 pt)

Show your calculation:

Theory IChO 2020

A6-6
English (Oﬃcial)6.12 (8.0 pt)

favored298 K8930 K
9005 K
9100 K
6.13 (6.0 pt)

Show your calculation:

□
□
□
□

Unfavored□□□□

Theory IChO 2020

Q7-1
English (Oﬃcial)

Phthalocyanines

The term phthalocyanine (Pc) takes its origin from the Greek “naphtha”, which means rock oil, and “cyanine”, which means dark blue. Turkish scientist Özer Bekaroğlu can be regarded as the pioneer of Pc
chemistry in Turkey.
Metal-free phthalocyanine (1, H2 Pc) is a large planar macrocyclic compound with the formula(C8 H4 N2 )4 H2 .
7.1

How many 𝜋-electrons are there in the bold region of the H2 Pc molecule in compound 1 shown above?

4.0pt

Theory IChO 2020

Q7-2
English (Oﬃcial)

Pcs containing one or two metal ions are called metallo-phthalocyanines (MPcs) and they exhibit different
geometries as given above.
7.2

Complete the table in your answer sheet by determining the coordination number of central ions in 2–5.

8.0pt

7.3

Complete the table in your answer sheet by determining the oxidation numberof each metal (Cu, Ti, and Ce) in 2, 3, and 5.

6.0pt

7.4

Complete the table in your answer sheet by determining the geometry of compounds 2–5.

8.0pt

7.5

Complete the table in your answer sheet by determining the magnetic property
of compounds 2–5.
• Use the letter "p" for paramagnetic property and letter "d" for a diamagnetic property.

8.0pt

7.6

Write the ground-state electron conﬁguration of the silicon (Si) ion in the compound 4, and ﬁnd all the quantum numbers for the 2p electrons in its groundstate.

14.0ptMetal-free phthalocyanine (1, H2 Pc) is commonly formed through the cyclotetramerization of phthalonitriles. On the other hand, Pcs having different substituents are called asymmetric, which can be preparedby the statistical cyclization of two different phthalonitriles. This method has no selectivity and the product is a mixture of all possible isomers.
7.7

Draw the possible products that may occur in the statistical cyclization methodby using F and G. If there are any stereoisomers label as cis- or trans-.
• F and G represent two different symmetrical phthalonitriles.
• One of the products is F4 as given below.
• Draw other products similar to the format in F4 .

19.0ptPcs are used as photosensitizers in the photodynamic therapy (PDT) of cancer due to their strong absorption in the visible spectrum and high molar absorption coeﬃcients. PDT consists of three essential

Theory IChO 2020

Q7-3
English (Oﬃcial)components: photosensitizer, light, and oxygen. None of these is individually toxic, but together they
initiate a photochemical reaction resulting in the generation of cytotoxic singlet oxygen (1 O2 ) that can
destroy cancer cells.
(multiplicity) 1 O2
• The multiplicity of an energy level is deﬁned as 2S+1
• If the two spins are parallel (↑↑), S = 1, and if the two spins are antiparallel (↑↓), S = 0.
7.8

Draw the molecule orbital (MO) diagram of the lowest energy singlet state ofdioxygen (1 O2 ) and calculate bond order.
• There are no unpaired electrons in that state!

12.0pt7.9

If the wavelength of the light needed to excite triplet oxygen into singlet oxygen is 1270 nm, calculate the energy (in kJ per mole) needed for this transition
process.

6.0pt

Theory IChO 2020

A7-1
English (Oﬃcial)

Phthalocyanines
7.1 (4.0 pt)

The number of 𝜋-electrons in an H2 Pc:

7.2 (8.0 pt)

Central ion

Copper ion

Titanium ion

Silicon ion

Cerium ion

Coordination number
7.3 (6.0 pt)

Metal in compounds

2

3

Oxidation number
7.4 (8.0 pt)

Geometry
Octahedral
Square prism
Square pyramidal
Square planar

Compound5

Theory IChO 2020

A7-2
English (Oﬃcial)

7.5 (8.0 pt)

CompoundMagnetic property

2345
7.6 (14.0 pt)

Electron conﬁguration:nQuantum numbers for 2p electrons:

l

m1

m𝑠

Theory IChO 2020

A7-3
English (Oﬃcial)

7.7 (19.0 pt)

Products:

Theory IChO 2020

A7-4
English (Oﬃcial)

7.8 (12.0 pt)

MO diagram:

Bond order:
7.9 (6.0 pt)

Show you calculation:

Energy = ……......………… kJ/mol

Theory IChO 2020

Q8-1
English (Oﬃcial)

Boron Compounds and Hydrogen Storage

Sodium borohydride (NaBH4 ) and ammonia borane (BNH6 ) are the most studied chemical hydrogen storage materials. In this question, you will explore the chemistry of boron and the use of boron compounds
as hydrogen storage materials.
Borax (Na2 B4 O7 ∙nH2 O) is a boron mineral that is produced by ETI Mining Company in Turkey. NaBH4 canbe synthesized by the reduction of anhydrous borax with metallic sodium under high-pressure hydrogengas in the presence of silicon dioxide (silica) at 700 °C, namely the Bayer process. In this process, allhydrogen is stored in NaBH4 . On the other hand, it has been shown that ammonia borane (BNH6 ) can besynthesized by the reaction of NaBH4 and ammonium sulfate in dry tetrahydrofuran (THF) at 40 °C (Hint:
BNH6 synthesis must be conducted in a well-ventilated fume-hood because ﬂammable gas is generated
as one of the by-products). While NaBH4 is an ionic compound, ammonia borane is a Lewis acid–baseadduct.
8.1

Write a balanced chemical equation for the synthesis of NaBH4 from anhydrous
borax.

3.0pt

8.2

Write a balanced chemical equation for the synthesis of ammonia borane from
NaBH4 .

3.0pt

8.3

Draw the molecular geometries of the BH−
4 ion and BNH6 molecule.

4.0pt

8.4

Calculate the hydrogen content of NaBH4 and BNH6 as a percentage by mass(wt%).

4.0pt

The hydrogen stored in both compounds can be released via hydrolysis reactions in the presence ofa suitable catalyst at room temperature. Upon the hydrolysis reactions, 4 and 3 moles of H2 gas are

Theory IChO 2020

Q8-2
English (Oﬃcial)released from the hydrolysis of 1 mole of NaBH4 and BNH6 , respectively, along with metaborate anion
including B-O bonds.
8.5

Write the balanced chemical equations for the hydrolysis of NaBH4 and BNH6 .

4.0pt

One of the simplest stable borates is diboron trioxide (B2 O3 ). Higher borates such as B3 O3−
6 having cyclic
structures containing B-O-bonds can be formed. Since B2 O3 is an acidic compound, it is easily reactedwith water to produce boric acid (H3 BO3 ). On the other hand, the high temperature and high-pressure
reaction of B2 O3 with ammonia yields two-dimensional boron nitride, which consists of planar graphitelike sheets of alternating B and N atoms.
8.6

Write the balanced chemical equations for the synthesis of boric acid and boron
nitride.

4.0pt

8.7

Draw the molecular structures of the B3 O3−
6 ion, boric acid, and a single twodimensional boron nitride sheet. Hint: show at least 10 B atoms in the boron
nitride structure.

6.0pt

Furthermore, B-H compounds, called boranes, are an important class of boron compounds. The simplest
stable borane is diborane (B2 H6 ) and many of the higher boranes can be prepared by the pyrolysis ofdiborane. Diborane can be synthesized via metathesis of a boron halide and a hydride source.
8.8

Write a balanced chemical equation for the synthesis of diborane from the reaction of BF3 and LiBH4 . Hint: both products are boron compounds.

3.0pt

8.9

Draw the molecular geometry of the diborane molecule. Hint: there is no B-B
bond in the molecule.

2.0pt

BH3 (borane) is an unstable and highly reactive molecule. Therefore, it is not possible to isolate it as BH3
under ordinary conditions. However, it can be stabilized via its reaction with carbon monoxide to yieldborane carbonyl (BH3 CO) compound, which is an adduct of borane. The preparation of BH3 CO plays animportant role in exploring the chemistry of boranes as it indicates the likely existence of the borane
molecule.
8.10

Sketch the Lewis dot structure of BH3 CO molecule by showing the formal
charges.

3.0pt

8.11

Which of the statements given in the answer sheet is observed in the C−O bondof a CO molecule upon the bond formation between BH3 and CO ? Tick thecorrect box.

2.0pt

Borazine consists of single and double bonded cyclic B−N units and hydrogen atoms attached to theseatoms with the molecular formula B3 N3 H6 and is isostructural to benzene. Borazine can be synthesized
by using a two-step procedure including the synthesis of symmetrically trisubstituted chlorine derivatives of borazine (B3 N3 H3 Cl3 ) from the reaction of ammonium chloride and boron trichloride, and thenreduction of B3 N3 H3 Cl3 with LiBH4 in THF.

Theory IChO 2020

Q8-3
English (Oﬃcial)

8.12

Write the balanced chemical equations for the two-step synthesis of borazine
starting from ammonium chloride in THF (tetrahydrofuran). Hint: THF stabilizes one of the products by forming a lewis acid-base adduct.

4.0pt

8.13

Draw the molecular structures of borazine and its symmetrically trisubstituted
chlorine derivative.

4.0pt

Catalysts are substances that accelerate the rate of reactions by allowing them to proceed in a lower
energy pathway. The catalytic activity of the catalysts is generally determined by the turnover frequency(TOF), which is calculated by dividing the molar amount of the product to the mole of active catalyst andthe time (TOF = mole product/(mole catalyst x time)). A typical hydrolysis of BNH6 was carried out in 10.0
mL of water by using 100.0 mM BNH6 and 5.0 mg of CuPt/C catalyst (CuPt alloy nanoparticles supported
on carbon black containing 8.2 wt% Pt atom).67.25 mL of hydrogen gas was generated in 5 minutes.
8.14

Assuming the catalytic reaction is performed in standard conditions (1atm and 273.15 K), calculate the TOF (min−1 ) of the CuPt/C catalyst
in terms of only Pt atoms in the hydrolysis of BNH6 by considering the volumeof the hydrogen gas generated.

4.0pt

As a result of detailed crystal analysis of a synthesized Cu𝑥 Pt𝑦 alloy nanoparticle (the subscripts indicate
molar percentages of the atoms in the alloy structure), it was determined that the face centered cubic(fcc) unit cell was formed by Pt atoms and the Pt atoms on the face of the fcc unit cell are supposed to be
replaced with Cu atoms to form Cu𝑥 Pt𝑦 displacement alloy nanoparticles. According to this information,
answer the following questions.
8.15

Determine the composition of the alloy nanoparticles by ﬁnding x and y in the
Cu𝑥 Pt𝑦 alloy composition.

2.0pt

8.16

Sketch the shape of the described crystal unit cell of Cu𝑥 Pt𝑦 alloy nanoparticles
by showing the placement of atoms on the unit cell.

2.0pt

8.17

Another alloy has a Cu2 Pt1 composition. Assume that this alloy also has an fcc
unit cell with an edge length of 380 pm, but the Cu and Pt atoms are randomly
distributed in the atomic positions. Calculate the density of this alloy in g/cm3 .

4.0pt

Theory IChO 2020

A8-1
English (Oﬃcial)

Boron Compounds and Hydrogen Storage
8.1 (3.0 pt)

8.2 (3.0 pt)

8.3 (4.0 pt)

8.4 (4.0 pt)

Theory IChO 2020

A8-2
English (Oﬃcial)

8.5 (4.0 pt)

8.6 (4.0 pt)

8.7 (6.0 pt)

B3 O3−
6

Boric acid

Boron nitride

Theory IChO 2020

A8-3
English (Oﬃcial)

8.8 (3.0 pt)

8.9 (2.0 pt)

8.10 (3.0 pt)

Theory IChO 2020

A8-4
English (Oﬃcial)8.11 (2.0 pt)

□
□
□
□

It gets longer because there will be 𝜋-back donation from BH3 to CO.
It gets longer because CO donates 𝜋-bonding electrons to BH3
No or slight change on it because CO donates its mainly non-bonding electrons to BH3
It gets shorter because CO donates 𝜋* anti-bonding electrons to BH3 .

8.12 (4.0 pt)

8.13 (4.0 pt)

8.14 (4.0 pt)

Theory IChO 2020

A8-5
English (Oﬃcial)8.15 (2.0 pt)

8.16 (2.0 pt)

8.17 (4.0 pt)

Theory IChO 2020

Q9-1
English (Oﬃcial)

Quantiﬁcation of Heavy Metal Ions
For the quantitative analysis of heavy metal ions in a factory’s wastewater pool, the following steps havebeen applied by an analyzer at 298 K:
Step 1) 10-mL samples of each were obtained from ﬁve different regions in a wastewater pool, mixed ina 100-mL beaker, and then stirred for 5 minutes using a magnetic stirrer.
Step 2) 10-mL of sample solution was taken from the 100-mL beaker and 142 mg of Na2 SO4 was added
while stirring, followed by transfer to a three-electrode cell as seen in Figure 1a. In this electrochemicalcell, Pt wire, Ag/AgCl (3 M KCl), and Pt foil served as the working, reference, and counter electrodes,
respectively.
Step 3) These electrodes were connected to a potentiostat and a constant potential of –0.50 V vs. Ag/AgClfor 14 minutes was applied as seen in Figure 1b (horizontal line). It is assumed that 14 min. is suﬃcient
to complete the expected electrochemical reactions.

Figure 1. a) Electrochemical cell design; 1) Working electrode (Pt wire), 2) reference electrode(Ag/AgCl, 3M KCl), 3) counter electrode (Pt foil), 4) cell tap, 5) electrochemical cell, 6) 10-mLof sample solution. b) Potential change of working electrode as a function of time. y-axis:
potential/V vs Ag/AgCl, x-axis: time/min.
Step 4) The electrodes were rinsed with distilled water, placed into another electrochemical cell including
10-mL of 0.1 M H2 SO4 solution, and potential was scanned between –0.50 and +0.50 V as seen in Figure
1b (downward sloping line in 2 min.). Current vs. potential data for this step are presented in Figure 2a,which is like an excellent view of Mount Ararat (Ağrı Dağı), the highest mountain in Turkey (Figure 2b).

Theory IChO 2020

Q9-2
English (Oﬃcial)

Figure 2. a) Potential scan of the working electrode as a function of current in 0.1 M H2 SO4
solution after keeping it constant at a potential of –0.50 V in 10-mL of wastewater sample asseen in Figure 1b (horizontal line). y-axis: current/𝜇A, x-axis: potential/V vs Ag/AgCl, b) A viewof Great and Little Ararat peaks.
Step 5) Another 10-mL of the sample solution prepared in step 1 was taken and the processes explainedin steps 2 and 3 were applied in that order. The electrodes were rinsed with distilled water and placed
into 10-mL of 0.1 M H2 SO4 solution. Then the potential of the working electrode was kept constant at+0.05 V for 14 min. It is assumed that 14 minutes is suﬃcient to complete the expected electrochemical
reactions.
Step 6) After step 5 was performed, the solution in the electrochemical cell was placed in a suitable ovento evaporate at 150 °C until dry solid was obtained.
Step 7) 5-mL of ethylenediaminetetraacetic acid (EDTA, H4 Y) (Figure 3) solution was added to the solid
obtained in step 6 and it was shaken to dissolve. It is known that 1-mL of EDTA solution is equivalent to3.85 mg/mL BaCO3 . Then, pH of the solution was adjusted to 10.0. Excess EDTA was titrated with standard 0.0010 M Ni(NO3 )2 solution and it was observed that 95.60 mL of Ni(NO3 )2 solution was consumed
up to the endpoint.

Theory IChO 2020

Q9-3
English (Oﬃcial)

Figure 3. Chemical structure of EDTA (H4 Y).
• In water saturated with H2 S, equilibrium concentration of [H2 S] is 0.1 M.
• K𝑠𝑝 (NiS) = 4.0 × 10–20 ; K𝑠𝑝 (CuS) = 1.0 × 10–36• K𝑎1 (H2 S) = 9.6 × 10–8 ; K𝑎2 (H2 S) = 1.3 × 10–14
Reaction

E˚/V (at 298 K)

2H2 O(l)+2e → H2 (g)+2OH (aq)

-0.83

Ni

(aq)+2𝑒 → Ni(s)

-0.24

−

2+

−

−

+

−

2H (aq)+2𝑒 → H2 (g)

0.00

2+

Cu

(aq)+2𝑒 → Cu(s)

+0.34

−

Ag+ (aq)+e− → Ag(s)+0.80

O2 (g)+4H (aq)+4e →2H2 O(l)

+1.23

+

−

9.1

Which of the following can be considered for peak 1 and peak 2 in Figure 2a,
respectively? Tick the correct box on the answer sheet.

5.0pt

9.2

Which of the statements is expected, if the potential is applied as –1.2 V insteadof –0.5 V at the ﬁrst step (horizontal line) in Figure 1b? Tick the correct box on
the answer sheet.

5.0pt

9.3

Calculate the scan rate of data presented in Figure 2a as mV/s at 298 K.

8.0pt

The potential of the following cell is measured as 0.437 V.
Pt,H2 (0.92 bar)|HCl(1.50×10−2 M),AgCl(sat)|Ag
9.4

Calculate the standard electrode potential value (V) of half-cell of AgCl(s)+e− →Ag(s)+Cl− (aq) at 298 K.
Note: You must show all works.

16.0pt9.5

Which of the statements is the main purpose of step 5 in this analysis? Tick thecorrect box on the answer sheet.

5.0pt

Theory IChO 2020

Q9-4
English (Oﬃcial)

9.6

Write net ionic equations for the complexation and the back titration reactionof step 7 on the answer sheet.

6.0pt

9.7

Calculate Ni2+ concentration as mg/L in the wastewater of the factory. Note:
You must show all works.

25.0pt9.8

Calculate the minimum pH value for starting the precipitation of Ni2+ ions inthe solution obtained in step 5 by passing saturated H2 S gas into the solution
until saturation. If you cannot solve question 9.7, use 20 mg/L Ni2+ sample forthis question. Note: You must show all works.

30.0ptTheory IChO 2020

A9-1
English (Oﬃcial)

Quantiﬁcation of Heavy Metal Ions
9.1 (5.0 pt)

□
□
□
□
□

Peak 1: electrochemical reduction of Ni / Peak 2: electrochemical reduction of Cu
Peak 1: electrochemical reduction of Cu / Peak 2: electrochemical reduction of Ni
Peak 1: electrochemical reduction of Ni / Peak 2: electrochemical oxidation of Cu
Peak 1: electrochemical oxidation of Ni / Peak 2: electrochemical oxidation of Cu
Peak 1: electrochemical oxidation of Cu / Peak 2: electrochemical oxidation of Ni

9.2 (5.0 pt)

□
□
□
□
□

NO evolution
NO2 evolution
Nitrogen evolution
Oxygen evolution
Hydrogen evolution

9.3 (8.0 pt)

Show your calculation:

Scan rate = ..................................................... mV/s

Theory IChO 2020

A9-2
English (Oﬃcial)

9.4 (16.0 pt)

Show your calculation:

Standard electrode potential =…………………… V
9.5 (5.0 pt)

□
□
□
□
□

Modiﬁcation of Pt wire with Ni–Cu alloy ﬁlm
Modiﬁcation of Pt wire with Ni ﬁlm
Electrochemical stripping of both Cu and Ni from Cu–Ni-modiﬁed Pt wire to the solution
Electrochemical stripping of Cu from Cu–Ni-modiﬁed Pt wire to the solution
Electrochemical stripping of Ni from Cu–Ni-modiﬁed Pt wire to the solution

9.6 (6.0 pt)

Complexation:

Back titration:

Theory IChO 2020

A9-3
English (Oﬃcial)

9.7 (25.0 pt)

Show your calculation:

Ni2+ concentration: …………............…………. mg/L:

Theory IChO 2020

A9-4
English (Oﬃcial)

9.8 (30.0 pt)

Show your calculation:

Minimum pH value: ………………………