Modern Analytical Techniques 2

Question 1

This question is about some carbonyl compounds with the molecular formula C5H10O.
An aldehyde with molecular formula C5H10O has a 13C NMR spectrum with three peaks.
The high resolution 1H NMR spectrum of this aldehyde has two peaks and neither of them is
split.
Deduce the displayed formula of this aldehyde.
Justify your answer by referring to both NMR spectra.

4 marks

Question 2

Data from the high resolution 1H (proton) NMR spectrum of the ester Q are shown in the
table.

Chemical shift (ppm)/Splitting pattern/Relative peak area
2.50/singlet/3
1.56/quartet/4
1.43/singlet/3
0.92/triplet/6

Part of the structure of Q is shown.
Complete the structure of Q.
Justify your answer by linking the proton environments in your structure to the relative peak
areas and the splitting pattern of the peaks.
—————————————–
H3C - C -
||
O

7 marks

Question 3

This question is about the analysis of organic compounds.
There are similarities and differences in the 13C NMR spectra and the high resolution 1H
NMR spectra of isomeric
organic compounds.
Compare the NMR spectra of propan-1-ol with those of propan-2-ol.
Include the number of peaks, relative peak areas and splitting patterns, where appropriate.
Chemical shift values are not required.

6 marks

Question 4

Which would react with phenylethanone but not with phenylethanal?

1 mark

Question 5

Give the steps to show how 2,4-dinitrophenylhydrazine could be used to distinguish
between phenylethanone and phenylethanal.

4 marks

Question 6

Compare and contrast the high resolution proton NMR spectra of phenylethanone and
phenylethanal.

6 marks

Question 7

What is the number of peaks in a 13C NMR spectrum of isoamyl acetate and of amyl
acetate?

1 mark

Question 8

Antifebrin was the trade name for N-phenylethanamide which was used as a painkiller until
paracetamol was discovered.
What is the number of peaks in a C-13 NMR spectrum of Antifebrin?

1 mark

Question 9

Name the compound responsible for the peak at a chemical shift of 0 ppm, stating its
purpose

2 marks

Question 10

Identify the proton environment that causes the peak at a chemical shift of 3.8 ppm by
circling it on
the diagram shown. Fully justify your answer.

3 marks

Question 11

This question is about the use of NMR spectroscopy to distinguish between isomers of
C6H12O2.
There are three other isomers of C6H12O2 which are carboxylic acids with five peaks in
their carbon-13 NMR spectra.
Draw the structural formula of two of these isomers.

2 marks

Question 12

This question is about the use of NMR spectroscopy to distinguish between isomers of C6H12O2.
Draw the skeletal formula of a cyclic diol isomer of C6H12O2 that has only two peaks in
its carbon-13 NMR spectrum.

1 mark

Question 13

Compound D contains a benzene ring.
Give the molecular formula of the species that causes the peak at m / z = 76 in the mass
spectrum of D.

1 mark

Question 14

Draw the structures of the three possible isomers of D containing a benzene ring.

2 marks

Question 15

The 13C NMR spectrum of compound D has four peaks.
Identify the structure of D. Justify your answer by labelling the different
carbon environments in all the structures possible.

3 marks

Question 16

This question is about the use of NMR spectroscopy to distinguish between isomers of
C6H12O2.
Tetramethylsilane (TMS) is a compound used as a standard when recording both 1H and 13C
NMR spectra.
Give the structural formula of TMS.

1 mark

Question 17

This question is about the use of NMR spectroscopy to distinguish between isomers of
C6H12O2.
Tetramethylsilane (TMS) is a compound used as a standard when recording both 1H and 13C
NMR spectra.
TMS is an inert and non-toxic compound. State two other reasons why TMS is suitable
for use as a standard when recording NMR spectra.

2 marks

Question 18

This question is about the use of NMR spectroscopy to distinguish between isomers of
C6H12O2
Draw the structural formulae of the two esters with formula C6H12O2 that each have only
two peaks, both singlets, in their high resolution proton NMR spectra. The relative peak
areas are 3:1 for both esters.

2 marks

Question 19

This question is about the use of NMR spectroscopy to distinguish between isomers of
C6H12O2
The high resolution proton NMR spectrum of another isomer of C6H12O2 is shown in figure 1. The ratios of the number of protons for the five sets peaks in the spectrum are given in figure 2. Show that all these data are consistent with the displayed formula shown in figure 3. Refer to the five
chemical shifts and explain two of the splitting patterns.

5 marks

Question 20

2 marks