+OHX

NuX NuNu−X−

NMR

Benchtop NMR for
Educational Experiments
YYO

O+ H2OHOYOO+N+NO

O+ HNEliminationReaction
Br2+NNH
O+NOOOThis experiment is designed to teach the practical aspects andOprinciplesof theHO++OH
HOelimination reaction:
H2SO42X

Nu+ X− of reaction conditions.
Isolation of organic compounds, effect
X Nu

Nu−

Total experiment time: 1.5 hours in aqueous,
2 hours inYacetone
YThe elimination reaction
involves the reaction of a halogenalkane
in the presence of heat and a base to produce an alkene.
OHCOH+O CH O

33H SOO 2,3-dibromo-3-phenylpropanoic
An example is the elimination
reaction ofacid
O to form 1-bromo-2-phenylethene that takesOO+
OH

24+ H2O++- N on the reaction+
place via an E1conditions. The reaction
is performed in the presence of potassium
HOor E2 reaction dependingO- NN

carbonate:
X Nu

X

Nu−NHO

OROO

Br+N+
NO

BrO

HOO+NOH2NBrYO+BrX−BrYO

NuBrO+O+N

H2N+NH can be used to measure the spectra of the starting material and reaction
Pulsar™, a 60MHz benchtop NMR spectrometer+
N- completed and no starting materials remain. The spectra of the starting material
product confirming that the reaction hasOO
CH3HC
2,3-dibromo-3 phenylpropanoic acid, along with the OHfinal
phenylethene
are shown in Figure 1.
CH+ product 1-bromo-2
33O

Figure 1. From top to bottom:
2,3-dibromo-3-phenylpropanoic acid,1-bromo-2-phenylethene spectra+BrBrOOROHBr

HO+CH3Br

H3C

spectrum of 1-bromo-2-phenylethene.

!

BrORBr

It is clear from these spectra that there
is no starting material present in theCH3OOBr

The 1-bromo-2-phenylethene has
tetramethylsilane (TMS) added as achemical shift reference material showing
a peak at 0ppm chemical shift.

HOBr!

The product formed can be either a cis- or trans- form of thecompound dependent on the solvent chosen for the reaction.
In acetone the yield is almost 98% cis form. Whereas in water
the yield is 20% cis and 80% trans form of the compound.
The peaks due to the different forms (trans peaks arehighlighted in blue, cis peaks in pink) are shown in Figure 2.
Pulsar is a cryogen-free benchtop NMR spectrometerthat can easily be sited in the Undergraduate Chemistrylaboratory allowing hands-on NMR for students.
A simple to use software interface and standard sampling
using 5mm NMR tubes enables a high throughput ofsamples in a busy laboratory.

Figure 2. Peaks in the spectrum of the reaction product due to cis(pink) and trans (blue) forms of the compound.

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magres@oxinst.com

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