Exam Reading: Students will have 15 minutes to read this exam
booklet before starting the exam. Do not write or calculate during
this period, otherwise YOU will be disqualified. The official English
version of this examination is available on request only forclarification.

Theoretical problems (official English version), 49th IChO 2017, Thailand

1

Theoretical Problems"Bonding the World with Chemistry"
49th INTERNATIONAL CHEMISTRY OLYMPIAD
Nakhon Pathom, THAILAND

Theoretical problems (official English version), 49th IChO 2017, Thailand

2General Instructions.
 Pages: This theoretical exam booklet contains 54 pages. There are 11 Problems in
total.
 Exam Reading: Students will have 15 minutes to read this exam booklet before starting
the exam. Do not write or calculate during this period, otherwise YOU will bedisqualified. The official English version of this examination is available on request
only for clarification.
 Exam Time: Students will have a total of 5 hours to complete the exam.
 Start/Stop: Students may begin as soon as the “Start” command is given and muststop your work immediately when the “Stop” command is announced.
 Failure to stop the task by 1 minute or longer after the “Stop” command has
been announced will lead to nullification of your theoretical exam.
 After the “Stop” command has been given, place your exam booklet back inyour exam envelope and wait at your seat. The Exam Supervisor will come pickup your exam paper.
 Answer sheets: All results and answers must be clearly written in the appropriate areaon the exam papers for grading. Only answers written in pen will be graded.
 Use only pens provided for you.
 You may use the backside of the sheets as scratch papers. They will not bemarked.
 Calculator: For any calculation, use only the 49th IChO calculator provided.
 Need Assistance: If you need assistance (e.g. more snacks or drinks or go to a
restroom), Waive the orange IChO flag provided on your table.

Theoretical problems (official English version), 49th IChO 2017, Thailand

3

Table of Content

Problem
No.

Title

Page

% of Total
Score

1

Production of propene using heterogeneous catalysts

5

6%

2

Kinetic isotope effect (KIE) and zero-point vibrationalenergy (ZPE)

9

6%

3

Thermodynamics of chemical reactions

15

6%

4

Electrochemistry

19

5%

5

Phosphate and silicate in soil

25

5%

6

Iron

30

6%

7

Chemical Structure Puzzles

35

6%

8

Silica Surface

41

5%

9

Into the Unknown

45

6%

10

Total Synthesis of Alkaloids

48

7%

11

Twist & Chirality

53

2%

Theoretical problems (official English version), 49th IChO 2017, Thailand

4

Problem 1

Problem 1

6% of the total

Total
Score

A
A1 A2 A3
4
1
2

B

C

7

6

Total
20

Problem 1: Production of propene using heterogeneous catalysts
Propene or propylene is one of the most valuable chemicals for the petrochemicalindustry in Thailand and around the world. One good example of the commercial use ofpropene is for the production of polypropylene (PP).

Part A.
Propene can be synthesized via a direct dehydrogenation of propane in the presence ofa heterogeneous catalyst. However, such a reaction is not economically feasible due to thenature of the reaction itself. Provide a concise explanation to each of the questions below.
Additional information: Hbond(C=C) = 1.77Hbond(C-C), Hbond(H-H) = 1.05Hbond(C-H), and
Hbond(C-H) = 1.19Hbond(C-C), where Hbond refers to average bond enthalpy of the indicatedchemical bond.
1-A1) What is the enthalpy change of the direct dehydrogenation of propane? Show yourcalculation and express your answer in terms of Hbond(C-C).
Calculation:

Theoretical problems (official English version), 49th IChO 2017, Thailand

5

1-A2) It is difficult to increase the amount of propene by increasing pressure at constanttemperature. Which law or principle can best explain this phenomenon? Select your answer bymarking “” in one of the open circles.
⃝ Boyle’s law⃝ Charles’ law⃝ Dalton’s law⃝ Raoult’s law⃝ Le Chatelier’s principle
1-A3) Initially, the system is in equilibrium. Consistent with question 1-A1), what is/are correctset(s) of signs for the following thermodynamic variables of the system for the direct
dehydrogenation of propane? Select your answer(s) by marking “” in any of the open
circle(s).
⃝
⃝
⃝
⃝
⃝
⃝
⃝
⃝
⃝
*

S
G T*
H
+
+
lower
+
higher+lower
higher
+
+
+
lower
+
+
higher++lower+
higherNone of the above is correct

Relative to the initial temperature at the same partial pressure.

Theoretical problems (official English version), 49th IChO 2017, Thailand

6

Part B.
A better reaction to produce large quantity of propene is the oxidative dehydrogenation(ODH) using solid catalysts, such as vanadium oxides, under molecular oxygen gas. Although
this type of reaction is still under intense research development, its promise toward the
production of propene at an industrial scale eclipses that of the direct dehydrogenation.
1-B) The overall rate of propane consumption in the reaction is rC3 H 8 

1

,




p
p



 k red pC Hkpox O2 3 8
where kred and kox are the rate constants for the reduction of metal oxide catalyst by propane
and for the oxidation of the catalyst by molecular oxygen, respectively, and p  is the standard
pressure of 1 bar. Some experiments found that the rate of oxidation of the catalyst is 100,000
pC H
times faster than that of the propane oxidation. The experimental rC3 H 8  k obs 3 8 at 600 K,
pwhere kobs is the observed rate constant (0.062 mol s-1). If the reactor containing the catalyst is
continuously passed through with propane and oxygen at a total pressure of 1 bar, determine
the value of kred and kox when the partial pressure of propane is 0.10 bar. Assume that the partialpressure of propene is negligible.
Calculation:

Theoretical problems (official English version), 49th IChO 2017, Thailand

7

Part C.
The metal oxide catalyst contains oxygen atoms on its surface that serve as active sites
for the ODH. Denoting red* as a reduced site and O(s) as an oxygen atom on the surface of thecatalyst, one of the proposed mechanisms for the ODH in the presence of the catalyst can be
written as follows:k1
C3H8(g) + O(s) 
C3H6(g) + H2O(g) + red*(1)

k2
C3H6(g) + 9O(s) 
3CO2(g) + 3H2O(g) + 9red*(2)

k3
O2(g) + 2red* 
2O(s)

(3)

Given  

number of reduced sites, the rate laws for the above 3 steps are:total number of active sites

r1  k1 pC3 H 8 (1   ) ,r2  k 2 pC3 H 6 (1   ) ,and r3  k 3 pO2  .
1-C) Assuming that the amount of oxygen atoms on the surface stays constant at any time ofreaction, calculate  as a function of k1, k2, k3, pC3 H 8 , pC3 H 6 , and pO2 .

Calculation:

Theoretical problems (official English version), 49th IChO 2017, Thailand

8

Problem 2

Problem 2

6% of the total

Total
Score

A
A1 A2 A3 A4 A5 A6 A7 A8
2
2
7
3
3
1
5
1

Total
24

Problem 2: Kinetic isotope effect (KIE) and zero-point vibrational energy (ZPE)
Calculation of ZPE and KIE
Kinetic isotope effect (KIE) is a phenomenon associated with a change in rate constantof the reaction when one of the atoms is replaced by its isotope. KIE can be used to confirm
whether a particular bond to hydrogen is broken in the reaction. Harmonic oscillator model isused to estimate the difference in the rate between C-H and C-D bond activation (D = 21H).
The vibrational frequency () represented by harmonic oscillator model is



1
2

k



,

where k is the force constant and is the reduced mass.
The vibrational energies of the molecule are given by1
E n   n   h ,2where n is vibrational quantum number with possible values of 0, 1, 2, ... The energy of thelowest vibrational energy level (En at n= 0) is called zero-point vibrational energy (ZPE).
2-A1) Calculate the reduced mass of C-H (CH) and C-D (CD) in atomic mass unit. Assume
that the mass of deuterium is twice that of hydrogen.

Calculation:[If students are unable to calculate the values for CH and CD in 2-A1), use CH = 1.008 andCD = 2.016 for the subsequent parts of the question. Note that the given values are notnecessarily close to the correct values.]

Theoretical problems (official English version), 49th IChO 2017, Thailand

92-A2) Given that the force constant (k) for C-H stretching is the same as that for the C-D
stretching and the C-H stretching frequency is 2900 cm-1, find the corresponding C-D
stretching frequency (in cm-1).

Calculation:

Theoretical problems (official English version), 49th IChO 2017, Thailand102-A3) According to the C-H and C-D stretching frequencies in question 2-A2), calculate thezero-point vibrational energies (ZPE) of C-H and C-D stretching in kJ mol-1.

Calculation:[If students are unable to calculate the values for ZPE in 2-A3), use ZPECH = 7.23 kJ/mol and
ZPECD = 2.15 kJ/mol for the subsequent parts of the question. Note that the given values are
not necessarily close to the correct values.]

Kinetic isotope effect (KIE)
Due to the difference in zero-point vibrational energies, a protonated compound and its
corresponding deuterated compounds are expected to react at different rates.
For the C-H and C-D bond dissociation reactions, the energies of both transition states
and both products are identical. Then, the isotope effect is controlled by the difference in the
ZPE's of the C-H and C-D bonds.

Theoretical problems (official English version), 49th IChO 2017, Thailand

112-A4) Calculate the difference in the bond dissociation energy (BDE) between C-D bond andC-H bond ( BDE CD  BDECH ) in kJ mol-1.

Calculation:

2-A5) Assume that the activation energy (Ea) for the C-H/C-D bond cleavage is approximately
equal to the bond dissociation energy and the Arrhenius factor is the same for both C-H and
C-D bond cleavage. Find the relative rate constant for the C-H/C-D bond cleavage (kCH/kCD) at
25 oC.
Calculation:

Theoretical problems (official English version), 49th IChO 2017, Thailand

12

Using KIE to study reaction mechanism
The oxidation of nondeuterated and deuterated diphenylmethanol using an excess ofchromic acid was studied.

1.00

1.00

0.90

0.90

0.80

0.80

0.70

0.70

ln (C0/Ct)

ln (C0/Ct)

2-A6) Let C0 be the initial concentration of either nondeuterated diphenylmethanol ordeuterated diphenylmethanol and Ct its concentration at time t. The experiment led to two plots(Figure 2a and Figure 2b), from which the first-order rate constant can be determined.

0.60
0.50
0.40

0.60
0.50
0.40

0.30

0.30

0.20

0.20

0.10

0.10
0.00

0.00
0

100

200
300
Time / min

400

500

Figure 2a

0

15

30

45
Time / min

60

75

90

Figure 2b

Which plot should be for the oxidation of nondeuterated diphenylmethanol and which one isfor the oxidation of deuterated diphenylmethanol?
For each statement, select your answer by marking “” in one of the open circles.
The oxidation of nondeuterated diphenylmethanol: ⃝ Figure 2a ⃝ Figure 2b
The oxidation of deuterated diphenylmethanol:⃝ Figure 2a ⃝ Figure 2b

Theoretical problems (official English version), 49th IChO 2017, Thailand13

2-A7) Determine kCH, kCD (in min-1), and the kCH/kCD of this reaction from the plots in question
2-A6).

Calculation:

2-A8) The mechanism has been proposed as follows:

According to the information in 2-A6) and 2-A7), which step should be the rate determining
step?
Select your answer by marking “” in one of the open circles.
⃝ Step (1)⃝ Step (2)⃝ Step (3)Theoretical problems (official English version), 49th IChO 2017, Thailand

14

Problem 3

Problem 3

6% of the total

Total
Score

A
A1 A2 A3
7
3
8

B

Total

6

24

Problem 3: Thermodynamics of chemical reactions
Part A.
Methanol is produced commercially by using a mixture of carbon monoxide andhydrogen over zinc oxide/copper oxide catalyst:
CO(g) + 2H2(g)  CH3OH(g).
The standard enthalpy of formation (Hfo) and the absolute entropy (So) for each of the threegases at room temperature (298 K) and at a standard pressure of 1 bar are given as follows.
GasHfo (kJ mol-1)

So (J K-1 mol-1)

CO(g)
H2(g)
CH3OH(g)

-111
0
-201

198
131
240

3-A1) Calculate Ho, So, Go, and Kp for the reaction at 298 K.
Calculation:

Ho= ………..………

kJ

So

= ………….……..

J K-1

Go

= ………..……….

kJ

Kp= ….…………….

If you are unable to calculate Kp at 298 K in problem 3-A1), use Kp = 9 × 105 later on.

Theoretical problems (official English version), 49th IChO 2017, Thailand

15

3-A2) A commercial reactor is operated at a temperature of 600 K. Calculate the value of Kp
at this temperature, assuming that Ho and So are independent of temperature.
Calculation:

Kp= ………………………..

If you are unable to calculate Kp at 600 K in problem 3-A2), use Kp = 1.0×10-2 later on.

Theoretical problems (official English version), 49th IChO 2017, Thailand

16

3-A3) Production of methanol in industry is based on flowing of the gas comprising 2.00 molesof H2 for each mole of CO into the reactor. The mole fraction of methanol in the exhaust gas
from the reactor was found to be 0.18. Assuming that equilibrium is established, what is thetotal pressure in the reactor at a high temperature of 600 K?
Calculation:

Total pressure = ………………………. bar.

Theoretical problems (official English version), 49th IChO 2017, Thailand

17

Part B.
3-B) Consider the following closed system at 300 K. The system comprises 2 compartments,
separated by a closed valve, which has negligible volume. At the same pressure P, compartment
A and compartment B contain 0.100 mol argon gas and 0.200 mol nitrogen gas, respectively.
The volumes of the two compartments, VA and VB, are selected so that the gases behave as ideal
gases.

After opening the valve slowly, the system is allowed to reach equilibrium. It is assumed
that the two gases form an ideal gas mixture. Calculate the change in Gibbs free energy at 300
K, G .
Calculation:

G= ………..………. J

Theoretical problems (official English version), 49th IChO 2017, Thailand

18

Problem 4

Problem 4

5% of the total

Total

A
A1
4

A2
1

A3
5

A4
6

Total
16

Score

Problem 4: ElectrochemistryPart A. Galvanic cell
The experiment is performed at 30.00ºC. The electrochemical cell is composed of a hydrogenhalf-cell [Pt(s)│H2(g)│H+(aq)] containing a metal platinum electrode immersed in a buffer
solution under a pressure of hydrogen gas. This hydrogen half-cell is connected to a half-cellof a metal (M) strip dipped in an unknown concentration of M2+(aq) solution. The two halfcells are connected via a salt bridge as shown in Figure 1.
Note: The standard reduction potentials are given in Table 1.

Figure 1 The galvanic cell

Theoretical problems (official English version), 49th IChO 2017, Thailand

19

Table 1. Standard reduction potential (range 298-308 K)
Half-reaction
Ba2+(aq) + 2eSr2+(aq) + 2eCa2+(aq) + 2eEr2+(aq) + 2eTi2+(aq) + 2eMn2+(aq) + 2eV2+(aq) + 2eCr2+(aq) + 2eFe2+(aq) + 2eCd2+(aq) + 2eCo2+(aq) + 2eNi2+(aq) + 2eSn2+(aq) + 2ePb2+(aq) + 2e2H+(aq) + 2eSn4+(aq) + 2eCu2+(aq) + eGe2+(aq) +2eVO2+(aq) + 2H+(aq) +eCu2+(aq) + 2eTc2+(aq) + 2eRu2+(aq) + 2eI2(s) + 2eUO22+(aq) + 4H+(aq)+ 2ePtCl42-(aq) + 2eFe3+(aq) + eHg22+(aq) + 2eHg2+(aq) + 2e2Hg2+(aq) + 2ePt2+(aq) + 2eMnO2(s) + 4H+(aq) + 2eCr2O72-(aq)+ 14H+(aq) + 6eCo3+(aq) + eS2O82-(aq) + 2e-

Ba(s)
Sr(s)
Ca(s)
Er(s)
Ti(s)
Mn(s)
V(s)
Cr(s)
Fe(s)
Cd(s)
Co(s)
Ni(s)
Sn(s)
Pb(s)
H2(g)
Sn2+(aq)
Cu+(aq)Ge(s)V3+(aq) + H2O(l)
Cu(s)
Tc(s)
Ru(s)
2I-(aq)U4+(aq) + 2H2O(l)Pt(s) + 4Cl-(aq)Fe2+(aq)
2Hg(l)Hg(l)Hg22+(aq)Pt(s)
Mn2+(aq) + 2H2O(l)2Cr3+ (aq) + 7H2O (l)Co2+(aq)
2SO42-(aq)Theoretical problems (official English version), 49th IChO 2017, Thailand

E๐ (V)-2.912-2.899-2.868-2.000-1.630-1.185-1.175-0.913-0.447-0.403-0.280-0.257-0.138-0.1260.000+0.151+0.153+0.240+0.337+0.340+0.400+0.455+0.535+0.612+0.755+0.770+0.797+0.851+0.920+1.180+1.224+1.360+1.920+2.01020

4-A1) If the reaction quotient (Q) of the whole galvanic cell is equal to 2.18 x 10-4 at 30.00๐C,
the electromotive force is +0.450 V. Calculate the value of standard reduction potential (E๐)
and identify the metal “M”.
Note; G  G o  RT ln Q
Calculations

The standard reduction potential of M is ……....………..………V(Answer with 3 digits after decimal point)
Therefore, the metal “M” strip is …………..………

4-A2) Write the balanced equation of the spontaneous redox reaction of the galvanic cell.

Theoretical problems (official English version), 49th IChO 2017, Thailand21

4-A3) The unknown concentration of M2+(aq) solution in the cell (Figure 1) can be analyzed
by iodometric titration. A 25.00 cm3 aliquot of M2+(aq) solution is added into a conical flask
and an excess of KI added. 25.05 cm3 of a 0.800 mol dm-3 sodium thiosulfate is required toreach the equivalent point. Write all the redox reactions associated with this titration andcalculate the concentration of M2+(aq) solution.

Calculations

The concentration of M2+(aq) solution is……….………mol dm-3
(answer with 3 digits after decimal point)

If student cannot find the answer, the student can use 0.950 mol dm-3 as the concentration of
M2+ for further calculations.

Theoretical problems (official English version), 49th IChO 2017, Thailand

22

4-A4) In Figure 1, if the hydrogen half-cell is under 0.360 bar hydrogen gas and the platinum
electrode is immersed in a 500 cm3 buffer solution containing 0.050 mol lactic acid (HC3H5O3)
and 0.025 mol sodium lactate (C3H5O3Na), the electromotive force of the galvanic cellmeasured is +0.534 V. Calculate the pH of the buffer solution and the dissociation constant(Ka) of lactic acid at 30.00๐C.

Calculations of pH of the buffer solution

pH of the buffer solution is ……………………………………
(answer with 2 digits after decimal point)
If student cannot find the answer, the student can use 3.46 as the buffer pH for further
calculations.

Theoretical problems (official English version), 49th IChO 2017, Thailand23

Calculations of the dissociation constant (Ka) of lactic acid

The dissociation constant of lactic acid is ……………………………………

Theoretical problems (official English version), 49th IChO 2017, Thailand

24

Problem 5

Problem
55% of the total

Total
Score

A
A1 A2
1
1

B
3

C
C1 C2
1
2

D
2

Total
10

Problem 5: Phosphate and silicate in soil
Distribution and mobility of phosphorus in soil are usually studied by sequential extraction.
Sequential extraction is performed by the use of acid or alkaline reagents to fractionate
inorganic phosphorus in soil. Soil sample was extracted and analyzed as follows:Part A. Determination of total phosphate (PO43-) and silicate (SiO44-)
A 5.00 gram of soil sample is digested to give a final volume of 50.0 cm3 digesting
solution which dissolves total phosphorus and silicon. The extract is analyzed for the total
concentrations of phosphorus and silicon. The concentrations of phosphorus and silicon arefound to be 5.16 mg dm-3 and 5.35 mg dm-3, respectively.
5-A1) Determine the mass of PO43- in mg per 1.00 g of soil.
Calculations

1 g of soil contains PO43- =mg (answer with 3 digits after decimal point)

5-A2) Determine the mass of SiO44- in mg per 1.00 g of soil.
Calculations

1 g of soil contains SiO44- =mg (answer with 3 digits after decimal point)

Theoretical problems (official English version), 49th IChO 2017, Thailand

25

Part B. Determination of available PO43- in acid extract
Phosphate can be analyzed by using molybdenum blue method. One mole of phosphate
is converted into one mole of molybdenum blue compound. This method is used for
determination of phosphate in the acid extract. Absorbance (A) and transmittance (T) arerecorded at 800 nm. The molar absorptivity of the molybdenum blue compound is 6720 dm3
mol-1 cm-1 and all measurement is carried out in a 1.00-cm cuvette.
Transmittance and absorbance are given by the following equations:
T = I / Io
A = log (Io / I)
where I is the intensity of the transmitted light and Io is the intensity of the incident
light.
5-B1) When the sample containing high concentration of phosphate is analyzed, a reference
solution of 7.5 x 10-5 mol dm-3 of molybdenum blue compound is used for adjusting zeroabsorbance. The transmittance of the sample solution is then measured to be 0.55. Calculate
the concentration of phosphate (mol dm-3) in the sample solution.

Calculations

 concentration of phosphate in an unknown sample =Theoretical problems (official English version), 49th IChO 2017, Thailand

mol dm-3

26

Part C. Determination of PO43- and SiO44- in alkaline extract
Both phosphate and silicate ions can react with molybdate in alkaline solution, producing theyellow molybdophosphate and molybdatosilicate. Further reduction with ascorbic acidproduces intense color molybdenum blue compounds. Both complexes exhibit maximum
absorption at 800 nm. Addition of tartaric acid helps preventing interference from silicate in
the determination of phosphate.
Two series of phosphate standard are treated with and without tartaric acid whereas a series ofsilicate standard is not treated with tartaric acid. Linear equations obtained from thosecalibration curves are as follows:
Conditions

Linear equations

Phosphate with and without tartaric acidy = 6720x1

Silicate without tartaric acidy = 868x2

y is absorbance at 800 nm,
x1 is concentration of phosphate as mol dm-3,
x2 is concentration of silicate as mol dm-3
Absorbance at 800 nm of the alkaline fraction of the soil extract after treated with and without
tartaric acid are 0.267 and 0.510, respectively.
5-C1) Calculate the phosphate concentration in the alkaline soil extract in mol dm-3 andcalculate the corresponding phosphorous in mg dm-3.
Calculations

 concentration of PO43- = concentration of P =mol dm-3

mg dm-3(answer with 2 digits after decimal point)

Theoretical problems (official English version), 49th IChO 2017, Thailand27

5-C2) Calculate the silicate concentration from the soil sample in t the alkaline fraction in mol
dm-3 and calculate the corresponding silicon in mg dm-3.
Calculations

 concentration of SiO44- =mol dm-3(answer with 2 digits after decimal point) concentration of Si =mg dm-3(answer with 2 digits after decimal point)

Theoretical problems (official English version), 49th IChO 2017, Thailand

28

Part D. Preconcentration of ammonium phosphomolybdate
A 100 cm3 of aqueous sample of ammonium phosphomolybdate ((NH4)3PMo12O40)
compound is extracted with 5.0 cm3 of an organic solvent. The organic-water partition coefficient(Kow) is defined as the ratio of the concentration of the compound in the organic phase (c o) tothat in the water phase (cw). Kow of the ammonium phosphomolybdate is 5.0. The molar
absorptivity of ammonium phosphomolybdate in the organic phase is 5000 dm3 mol-1 cm-1.

5-D) If the absorbance in the organic phase is 0.200, calculate the total mass of phosphorus (inmg unit) in the original aqueous sample solution. The optical pathlength of the cuvette is 1.00cm.
Calculations

total amount of P in the original aqueous solution =Theoretical problems (official English version), 49th IChO 2017, Thailandmg

29

Problem 6

Problem 66% of the total

Total
Score

A
A1
3

A2
8

B1
4

B
B2
3.5

C
B3
5

C1
2

C2
4

Total
29.5

Problem 6: Iron
Iron (Fe) is the fourth most abundant element in the Earth’s crust and has been used for morethan 5,000 years.
Part A.
Pure iron is easily oxidized, which limits its utilization. Element X is one of the alloying
elements that is added to improve the oxidation resistance property of iron.
6-A1) Below is some information about the element X:(1) In first ionization, an electron with quantum numbers n1 = 4 – l1 is removed.
(2) In second ionization, an electron with quantum numbers n2 = 5 – l2 is removed.
(3) The atomic mass of X is lower than that of Fe.
What is the element X?
(Answer by writing the proper symbol according to the periodic table.)

Theoretical problems (official English version), 49th IChO 2017, Thailand30

6-A2) Both Fe and X crystallize in the body centered cubic structure. Approximating the Featoms as hard-spheres, the volume taken up by the Fe atoms inside the unit cell is 1.59x10-23
cm3. The volume of the unit cell of X is 0.0252 nm3. A complete substitutional solid solution|𝑅 −𝑅 |
usually occurs when R = ( 𝑋𝑅 𝐹𝑒 ) × 100 is less than or equal to 15, where RX and RFe are𝐹𝑒the atomic radii of X and Fe, respectively. Can X and Fe form a complete substitutional solid
solution? Show your calculation. No credit is given without calculation presented. The
volume of sphere is 4/3r3.
Answer (Mark  in an appropriate box.)
 Yes (R  15)

 No (R > 15)

Calculation

RFe = ...…………...…..nm……………..…..

RX = ………………….nm

R =Theoretical problems (official English version), 49th IChO 2017, Thailand

31

Part B.
Iron in natural water is in the form of Fe(HCO3)2, which ionizes to Fe2+ and HCO3-. To remove
iron from water, Fe(HCO3)2 is oxidized to an insoluble complex Fe(OH)3, which can be filteredout of the water.
6-B1) Fe2+ can be oxidized by KMnO4 in a basic solution to yield Fe(OH)3 and MnO2
precipitates. Write the balanced ionic equation for this reaction in a basic solution.

Under this condition, HCO3 ions are converted to CO32. Write the balanced ionic equation
for this reaction in a basic solution.

6-B2) A covalent compound A which contains more than 2 atoms and, a potential oxidizing
agent, can be prepared by the reaction between diatomic halogen molecule (Q2) and NaQO2.
1Q2 + xNaQO2  yA + zNaQ
where x+y+z ≤ 7
where x, y and z are the coefficients for the balanced equation. Among the binary compounds
between hydrogen and halogen, HQ has the lowest boiling point. Identify Q and if A has an
unpaired electron, draw a Lewis structure of compound A with zero formal charge on all atoms.
(Answer by writing the proper symbol according to the periodic table.)Q = ……………........
Lewis structure of compound A

What is the molecular geometry of compound A? (Mark  in an appropriate box.)
 linear bent cyclic

 tetrahedral

 trigonal planar

Theoretical problems (official English version), 49th IChO 2017, Thailand other32

6-B3) Compound D is an unstable oxidizing agent that can be used to remove Fe(HCO3)2 fromnatural water. It consists of elements G, Z and hydrogen and the oxidation number of Z is +1.
In this compound, hydrogen is connected to the element having the higher electronegativity
among them. Below is some information about the elements G and Z:(1) G exists in its normal state as a diatomic molecule, G2.
(2) Z has one proton fewer than that of element E. E exists as a gas under standard
conditions. Z2 is a volatile solid.
(3) The compound EG3 has a pyramidal shape.
Identify the elements G and Z and draw a molecular structure of compound D.
(Answer by writing the proper symbol according to the periodic table.)G = …….………….……

Z = ……………….…..

Molecular structure of compound D

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Part C.
59
Fe is a radiopharmaceutical isotope which is used in the study of iron metabolism in the
spleen. This isotope decays to 59Co as follows:
59
59
26𝐹𝑒  27𝐶𝑜

+ a + b(1)

6-C1) What are a and b in equation (1)? (Mark  in the appropriate boxes.)
protonneutronbeta

positron

alpha

gamma

6-C2) Consider equation (1), if the 59Fe isotope is left for 178 days which is n times of its halflife (t1/2), the mole ratio of 59Co to 59Fe is 15:1. If n is an integer, what is the half-life of 59Fe
in day(s)? Show your calculation.
Calculation:

Half-life of 59Fe = …………………….days (1 decimal place)

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Problem 7
6% of the total

Problem 7
Total
Score

A
A1
4.5

A2
1.5

A3
6

Total
A4
6

A5
2

20

Problem 7: Chemical Structure Puzzles
Titanium complexes have been investigated for their antitumor activity. Many factors includingisomerism and sizes have shown to affect the potency of the complexes. This question deals
with the synthesis and characterization of some titanium complexes.
7-A1) A reaction of 2 equivalents of 2-tert-butylphenol, 2 equivalents of formaldehyde, and
N,N'-dimethylethylene-1,2-diamine under acidic conditions at 75 C affords three major
products with the same chemical formula of C26H40N2O2, as shown in the equation below.
Draw the structure of each product.

Product 1:

Product 2:

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Product 3:

7-A2) If 2,4-di-tert-butylphenol is used as a substrate instead of 2-tert-butylphenol using thesame stoichiometry as that in 7-A1), only one product X was obtained. Draw the structure of
X.

Theoretical problems (official English version), 49th IChO 2017, Thailand36

A reaction between X from 7-A2) and Ti(OiPr)4 [iPr = isopropyl] in diethyl ether under an inert
atmosphere resulted in the six-coordinate Ti complex Y, as a yellow crystalline solid andisopropanol at room temperature.

(equation 1)
UV-Vis spectra of X, Ti(OiPr)4, and Y reveal that only the product Y has an absorption at  =370 nm. By varying the volumes of X and Ti(OiPr)4, each with the concentration of 0.50 mol
dm-3, and using benzene as the solvent, the absorbance data at  = 370 nm are given below:
Volume of X
(cm3)
0
0.20
0.30
0.50
0.78
0.90
1.10
1.20

Volume of Ti(OiPr)4
(cm3)
1.20
1.00
0.90
0.70
0.42
0.30
0.10
0

Volume of benzene
(cm3)
1.80
1.80
1.80
1.80
1.80
1.80
1.80
1.80

Absorbance
0.05
0.25
0.38
0.59
0.48
0.38
0.17
0.02

7-A3) Fill in appropriate values in the table provided below.

mole of X
mole of X + mole of Ti(Oi Pr)4

Absorbance
0.05
0.25
0.38
0.59
0.48
0.38
0.17
0.02

(2 digits after the decimal)

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Plot a graph showing a relationship between

mole of X
and absorbancemole of X + mole of Ti(Oi Pr)4in the space provided below.
1.00
0.90
0.80

Absorbance

0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

mole of X
mole of X + mole of Ti(OiPr)4mole of X
which maximizes the amount of the product Y
mole of X + mole of Ti(Oi Pr)4
represents the stoichiometry of X in the chemical formula of Y. Based on the graph above,
what is the molar ratio between Ti:X in the complex Y?
The value of

The molar ratio between Ti:X in the complex Y is ................................................

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7-A4) The Ti complex Y is six-coordinated. The IR spectrum of Y does not contain a broad
absorption band in the range of 3200–3600 cm-1. Y exists as three diastereomers. Ignoring
stereochemistry at N atoms, draw clearly the structures of all three diastereomers.
Note that you do not need to draw the complete structure of the ligand. Only identify donor
atoms that involve in coordination with titanium and the ligand framework between the donor
atoms can be drawn as follows:
For example:

can be drawn as:**If you did not get a structure of X from 7-A2), use the following ligand symbol to represent
X (A and Z are donor atoms):

Diastereomer 1:

Diastereomer 2:

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Diastereomer 3:

7-A5) Under certain conditions, the reaction shown in equation 1 affords only one
diastereomer of Y. Given that structures of Y are "fixed" (no intramolecular movement), the1
H NMR spectrum of Y in CDCl3 shows four singlet resonances at  1.25, 1.30, 1.66, and 1.72
corresponding to the tert-butyl groups. Draw a structure of the only possible diastereomer ofY.
(You do not need to draw the complete structure of the ligand. Only identify donor atoms thatinvolve in coordination and the ligand framework between the donor atoms can be drawn asshown in 7-A4))

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Problem 8

Problem 8

5% of the total

Total
Score

A1
6

A2
5.5

A
A3
3

A4
4

A5
1.5

Total
20

Problem 8: Silica Surface
Silica exists in various forms like amorphous and crystalline. Silica can be synthesized via solgel process by using silicon alkoxides like tetramethoxysilane (TMOS) and tetraethoxysilane(TEOS) as the details below:
a. Hydrolysis

b. Water condensationc. Alcohol condensation

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In bulk silica, all silicon atoms are tetrahedrally bonded to four oxygen atoms giving threedimensional solid network. The silicon environments found inside silica is presented below:

8-A1) Three silicon atom environments (similar to the example above) are commonly
observed at the silica surface. The three structures of the silicon environments must be drawn
in the provided boxes.

Silica can be used as an effective metal ion adsorbent in water. The proposed structure formetal-silica complex is as follows:
z

y
x
I

II

8-A2) After Cu2+ is being adsorbed, the color of silica changes from white to pale blue. The
visible spectrum shows a broad absorption band (with a shoulder) at max = 550 nm. If Cu2+
can bind with silica and adopt the structure similar to II, draw the splitting diagram of the dorbitals of Cu2+ ion including the label of the d orbitals in the complex and specify thecorresponding electronic transition(s) for the visible absorption.
The splitting diagram:

The corresponding electronic transition(s) (indicate the lower energy d-orbital andhigher energy d-orbital)

Theoretical problems (official English version), 49th IChO 2017, Thailand42

8-A3) If the first row transition metal ions form complexes with silica analogous to Cu2+,
which metal ion(s) do(es) have the analogous to electronic transition(s) to Cu2+? The metalion(s) must be in +2 or +3 oxidation state. Please note that the silanol groups (Si-OH) and water
are weak field ligands.

However, silica is randomly bonded to various types of metal ion. To increase the selectivity,
modification of silica surface has been performed by grafting with various organic molecules
like 3-aminopropyltrimethoxysilane and 3-mercaptopropyltrimethoxysilane.

8-A4) If Hg2+ is only bonding to sulfur binding sites in silica-SH, the symmetric complexof [Hg(silica-SH)2]2+ is formed. Draw the structure of [Hg(silica-SH)2]2+, specify the directionof the bond axes, and draw the corresponding d-orbital splitting. (You may use R-SH insteadof drawing the whole structure of silica-SH.)The structure:d-orbital splitting diagram :Theoretical problems (official English version), 49th IChO 2017, Thailand

43

8-A5)

Specify true or false for the following statements:a) d-d transition is found in [(Hg(silica-SH)x)]2+
 True Falseb) The [Cu(silica-NH2)x]2+ in a similar geometry, is expected to have a color similar
to other copper(II) amine complexes.
 True Falsec) In the visible absorption spectra, max of [Cu(silica-NH2)x]2+ is greater than thatof [Cu(silica-OH)x]2+.
 True False

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Problem 9

Problem 96% of the total

Total
Score

A1
6

A
A2
6

A3
11

Total
23

Problem 9: Into the Unknown
9-A1) Organic compound A is chiral and contains only three elements with the molecularweight (MW) of 149 (rounded to an integer).
1

H NMR spectrum of compound A shows among others, three types of aromatic
protons, and its 13C NMR spectrum shows eight signals, of which four signals are in the rangeof 120-140 ppm.
Compound A can be prepared by treating a carbonyl compound with methylamine
followed by NaBH3CN. Write all possible structural formulae of compound A. No
stereochemistry is required, and do not include stereoisomers.

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9-A2) One of the position isomers of compound A (structure A1, A2 or A3) can be synthesizedfrom compound B or C and D as shown in the diagram below. Write down the structural
formulae of compounds B-F, and the position isomer of compound A.

Theoretical problems (official English version), 49th IChO 2017, Thailand46

9-A3) Compound A is the (R)-form of one of structures A1-A3. It can be prepared from vicinal
diols X and Y as shown in the diagram below. Both diols are structural isomers, and eachstructure contains one carbon less than that of compound A. Write down the structural formulaeof compounds G-N, X, Y and the (R)-form of compound A. You must show stereochemistryof all compounds.

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Problem 10
7% of the total

Problem 10
Total
Score

A
A1
20.5

B
B1
4

B2
5.5

Total
30

Problem10: Total Synthesis of Alkaloids
Alkaloids are a class of nitrogen-containing natural products. Their structural complexityand potent biological activities has drawn attentions. Two representative examples of alkaloids–sauristolactam and pancratistatin are highlighted in following questions.
Part A
Sauristolactam possesses excellent cytotoxicity against various cancer cell lines. It could be
prepared by following synthetic sequence below. (1H-NMR spectra were recorded in CDCl3 at
300 MHz.)

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48

10-A1) Draw the structures of A-G in the sequence. Provide your answers on the following
blank sheet.

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49

The structures of A-G.

A

B

C

D

E

F

G

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50

Part B
Pancratistatin, isolated from a Hawaiian native plant, spider lily, exhibits potent in vitro and invivo inhibitory activity of cancer cell growth in addition to its excellent antiviral activity.

Pancratistatin could be successfully synthesized via intermediates X1 and X2. The synthesis ofthese intermediates are shown in the following schemes.
10-B1) Draw the structures of A and B.

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10-B2) Intermediate X1 (a single enantiomer with the stereochemistry shown) is labeled with
deuterium with configuration as indicated below, propose the 3-D chair structure of compound
E and the structure of compound F, with stereochemistry. Is Y a proton (1H) or a deuterium(2H)?

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Problem 11
2% of the total

Problem 11
Total
Score

A
A1
10

A2
2

Total
12

Problem 11: Twist & Chiralitytrans-Cyclooctene has a chiral plane and a high barrier for racemization. The double bond oftrans-cyclooctene is twisted, as a result, the molecule displays unusual reactivity incycloaddition reactions.
In 2011, Fox and coworkers developed a photochemical synthesis towards a variety of transcyclooctene derivatives. The process is non-stereocontrolled and the synthetic scheme is asfollow.

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11-A1) Draw all possible stereoisomers of compound 3 that could be obtained from thereduction of compound 2. Not necessary to assign R,S configuration.

11-A2) If one of the stereoisomers of compound 3 is converted to compound 4, how many
stereoisomeric form(s) of compound 4 will be obtained?
Number of possible stereoisomeric form(s) of compound 4 =If there are more than one stereoisomer, is it possible to separate the obtained
stereoisomers of compound 4 by achiral chromatography?

 Yes

 No

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