NGEE ANN POLYTECHNIC
FEBRUARY 2009 EXAM
School of Life Sciences and Chemical Technology
(Certificate in Chemistry)
Time Allowed: 2 Hours
MOLECULAR CHARACTERISATION METHODS
(008197)
INSTRUCTIONS TO CANDIDATES:
1.
Please read instructions carefully.
2.
Write ALL answers in the answer booklet provided.
3.
This paper consists of 7 questions, and all questions should be attempted.
4.
This paper consists of 7 pages including this cover page. Please check
carefully to make sure your set is complete.
5.
The following information may also be used:
Atomic weights: C: 12; H: 1; O: 16; N: 14
Formula for number of rings and double bonds for a molecule CxHyOz:
No of rings+double bonds = x+1- (y/2)
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Feb 2009
Answer all questions
Question 1
Identify the circled pair of protons (Fig 1) as unrelated, homotopic, enantiotopic or
diastereotopic and give your reasons(s).
(3 marks)
OH
H
H3C
CH3
H
H H
H
Figure 1
Question 2
Predict and sketch the coupling pattern of the circled proton (Fig 2) in the proton NMR of
the compound below and give your reasoning.
(5 marks)
Cl
H
H
Figure 2
Question 3
Draw the predicted detectable fragments in the mass spectrum of the ketone below (Fig
3) if it undergoes
(12 marks)
(a) the McLafferty rearrangement
(b) alpha cleavage
Note: You do not need to calculate the molecular weights of the fragments.
H
CH3
O
CH3
Figure 3
Question 4
You have a bottle labelled ‘benzene’ but you suspect it contains toluene (Fig 4) instead.
How would you use IR, proton NMR and 13-C NMR to tell which chemical it is?
Explain your answers fully.
(15 marks)
CH3
Benzene
Toluene
Figure 4
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Feb 2009
Question 5
Compound X has the empirical formula C4 H10 O
Study the IR, 13-C, proton NMR and mass spectra of compound X (Fig 5a-c)
Identify compound X. Explain your reasoning and assign as many peaks in the 13-C and
proton NMR spectra as you can.
(20 marks)
Spectroscopic Information for compound X
MS (Figure 5a): m/z 74
IR (Figure 5b): 3328 (br, s); 2958 (s); 1471 (m); 1387 (m); 1247 (w);1042 (s) cm-1
13C NMR (Figure 5c – on top): 69.2, 30.8, 18.9 ppm (NB – the triplet at about 75 ppm is
the solvent CDCl3)
Proton NMR (Figure 5c – below): 3.4 ppm (2H, doublet of doublet, J=4.9, 2 Hz); 2.4
ppm (1H, triplet, J=2 Hz); 1.75 ppm (1H, multiplet); 0.92 ppm (6H, doublet, J=5.5 Hz)
Question 6
Compound Y has the empirical formula C8 H10 O
Study the IR, 13-C, proton NMR and mass spectra of compound Y. (Fig. 6a-c)
Identify compound Y and explain your reasoning.
(20 marks)
Spectroscopic Information for compound Y
MS (Figure 6a): m/z 122
IR (Figure 6b): 3060 (w), 3047 (w), 2981 (m), 1602 (s), 1498 (s) cm-1
13C NMR (Figure 6c – on top): 158.9 (v weak), 129.4, 129.5, 114.5, 63.2, 14.8 ppm (NB
– the triplet at about 75 ppm is the solvent CDCl3)
Proton NMR (Figure 6c – below): 6.8-7.4 ppm (5H, multiplet); 4.0 ppm (2H, quartet, J=4
Hz); 1.4 ppm (3H, triplet, J=4 Hz)
Question 7
Compound Z has the empirical formula C6 H12 O
Study the IR, 13-C, proton NMR and mass spectra of compound X.
(a) Identify compound Z. Explain your reasoning.
(b) Assign the peaks in the mass spectrum at m/z 43, 58 and 85
(25 marks)
Spectroscopic Information for compound Z
MS (Figure 7a): m/z 100, 85, 58, 43
IR (Figure 7b): 2974 (m), 1714 (vs) cm-1
13C NMR (Figure 7c – on top): 208.5 (v weak), 52.8, 30.3, 24.7, 22.5 ppm
(NB – the triplet at about 75 ppm is the solvent CDCl3)
Proton NMR (Figure 7c – below): 2.32 ppm (2H, doublet, J=4 Hz); 2.15 ppm (1H,
multiplet); 2.12 ppm (3H, singlet); 0.95 (6H, doublet, J=5 Hz)
-END OF PAPER -
MCM (CCI)
3
Feb 2009