+
OH
X
Nu
X Nu
Nu−
X−
NMR
Benchtop NMR for
Educational Experiments
Y
Y
O
O
+ H2O
HO
Y
O
O
+
N
+
N
O
O
+ HN
Elimination
Reaction
Br
2
+
N
NH
O
+
N
O
O
O
This experiment is designed to teach the practical aspects andOprinciples
of the
HO
+
+
OH
HO
elimination reaction:
H2SO4
2
X
Nu
+ X− of reaction conditions.
Isolation of organic compounds, effect
X Nu
Nu−
Total experiment time: 1.5 hours in aqueous,
2 hours inYacetone
Y
The elimination reaction
involves the reaction of a halogenalkane
in the presence of heat and a base to produce an alkene.
O
HC
OH
+
O CH O
3
3
H SO
O 2,3-dibromo-3-phenylpropanoic
An example is the elimination
reaction of
acid
O to form 1-bromo-2-phenylethene that takes
O
O
2
4
+ H2O
+
+
+
- N on the reaction
+
place OH
via an E1
conditions. The reaction
is performed in the presence of potassium
HOor E2 reaction depending
O
- N
N
carbonate:
X Nu
X
Nu−
NH
O
OR
O
O
Br
+
N
+
N
O
Br
O
HOO
+
N
O
H2N
Br
Y
O
+
Br
X−
Br
Y
O
Nu
Br
O
+
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 has
O
O
CH3
HC
2,3-dibromo-3 phenylpropanoic acid, along with the OH
final
phenylethene
are shown in Figure 1.
CH
+ product 1-bromo-2
3
3
O
Figure 1. From top to bottom:
2,3-dibromo-3-phenylpropanoic acid,
1-bromo-2-phenylethene spectra
+
Br
Br
O
OR
OH
Br
HO
+
CH3
Br
H3C
spectrum of 1-bromo-2-phenylethene.
!
Br
OR
Br
It is clear from these spectra that there
is no starting material present in the
CH3
O
O
Br
The 1-bromo-2-phenylethene has
tetramethylsilane (TMS) added as a
chemical shift reference material showing
a peak at 0ppm chemical shift.
HO
Br
!
The product formed can be either a cis- or trans- form of the
compound 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 are
highlighted in blue, cis peaks in pink) are shown in Figure 2.
Pulsar is a cryogen-free benchtop NMR spectrometer
that can easily be sited in the Undergraduate Chemistry
laboratory allowing hands-on NMR for students.
A simple to use software interface and standard sampling
using 5mm NMR tubes enables a high throughput of
samples 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.
Contact us now for more information
[email protected]
for more information visit www.oxford-instruments.com/pulsar
2927
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