ORGANIC CHEMISTRY TUTORIAL SHEET
2nd YEAR
Organic Spectroscopy
Reading:
Harwood and Claridge. Introduction to Organic Spectroscopy, OCP 43
Clayden, Greeves, Warren and Wothers, Organic Chemistry Chap 3, 11 and 15
Williams and Fleming, Spectroscopic Methods in Organic Chemisry
Topics for notes:
NMR is the most important spectroscopic technique in chemistry. Your notes should concentrate
on the interpretation of spectra and the use of NMR in determining structures.
NMR Spectroscopy: Observable Nuclei.
Spin, sensitivity, abundance, high and low field.
1
H NMR: Shift range, (de)shielding, effect of hybridization, first order
coupling patterns, “roofing” in AB quartets, coupling constants, Karplus
curve, integration.
13
C NMR: Shift range, effect of hybridization, integration, coupling patterns,
decoupling, isotope effects.
Solvents, slow and fast exchange (and why this is useful) in hydrogen
bonding and conformational equilibria.
Homotopic, diastereotopic and enantiotopic, ring currents and aromaticity,
magnetic and chemical equivalence.
Modern techniques: the basics of nOe-spectra, DEPT, 2-D spectra (COSY).
IR Spectroscopy:
Physical basis of vibrational spectroscopy, absorptions of major functional
groups, carbonyl groups and the effects of conjugation / strain, etc.
Mass spectroscopy:
Isotope patterns, fragmentation patterns, odd number nitrogen rule
UV Spectroscopy:
The very basics of energy transitions and chromophores
Polarimetry:
The very basics of optical rotation
2nd YEAR
ORGANIC SPECTROSCOPY
Tutorial Problems
1. Assign chemical shift values (in CDCl3) to the hydrogen atoms in the compounds below using
the following list (in ppm): 0.0, 1.43, 2.17, 3.30, 5.30, 7.37, 9.50
O
CH2Cl2
Me4Si
Me
Me
Me
O
Me
2. Draw the expected 1H NMR spectra of the following compounds: diethyl ether,
o-dichlorobenzene, dimethylformamide, 2-butanol. (give approximate chemical shift, multiplicity
and integral)
3. Draw the expected 1H NMR spectra of the following compounds:
O
Me
OMe
O
Me
O
O
OMe
OMe
HO
OMe
OH
OH
A
(assume no OH coupling)
4. Draw the 13C NMR spectra for cyclopentane, propanol, toluene, and A from question 3.
[draw 1H-decoupled 13C spectra; assume none of the peaks accidently overlap; give approximate
chemical shifts]
5. Identify the following unknown compounds – work out double bond equivalents first.
A: C7H12O2
IR 3300 (br), 1720, 1640 cm-1
1
H NMR δ 1.7 (3H, s), 1.8 (3H, s), 2.0 (2H, dt, J 6.0, 7.0 Hz), 2.36 (2H, t, J 7.0 Hz), 5.1 (1H,
t, J = 6.0 Hz), 10.5 (1H, exchanges with D2O)
B: C7H12O2
IR 1745 cm-1
1
H NMR δ 1.24 (6H, s), 1.6 (2H, t, 7.0 Hz), 1.7 (2H, m), 4.31 (2H, t, 7.0 Hz)
6. Assign the three DEPT-edited 13C spectra (1-3) below to the three compounds B, C and D,
briefly stating your reasoning.
O
O
O
O
O
OMe
B
C
O
D
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ORGANIC SPECTROSCOPY
2nd YEAR
7. Account for the observed proton decoupled one dimensional 13C spectrum 4 of compound E.
F
E
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2nd YEAR
ORGANIC SPECTROSCOPY
8. Two compounds F and G with the same molecular formula (C6H12O2) and same IR signal (1740
cm-1) gave mass spectra 5 and 6 below. Deduce the structures of F and G.
9. Give complete assignments for the non-aromatic carbons (A-J) of this compound. The
multiplicities refer only to one-bond C-H splitting. Explain your assignments.
[In this question the multiplicities of the 13C resonances indicate 13C-1H coupling, so for example “d”
means the carbon couples directly to one proton. “JCP” is a carbon-phosphorous coupling
constant.
δC (ppm)
multiplicity from
proton coupling
31
21.9
41.3
51.8
61.0
65.8
q
dd
d
d
d
JCP = 161 Hz
-
P coupling
68.5
d
-
69.0
69.3
173.2
207.3
t
t
s
s
JCP = 7Hz
JCP = 7 Hz
-
comments
OH
B
H
F
A
C
coupled to proton at δH = 4.19
(dq, JHH = 6.5, 6.2 Hz)
coupled to proton at δH = 4.01
(ddd, JHH = 2.0, 7.1, 6.9 Hz)
O
E
D
N
G
O
H
P
O
I
OCH2Ph
OCH2Ph
J
10. The 1H NMR spectrum of this compound has a 2 H singlet at –0.5 ppm. What does this this
imply about its electronic structure.
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2nd YEAR
ORGANIC SPECTROSCOPY
11. Identify the unknowns, A, B, C and D using the listed data.
A; C6H6O
νmax 3601, 3360, 3050, 1600, 750, 690
m/z 94 (100), 66 (19), 65 (17)
CHCl3, NaOH, water
B; C7H6O2
νmax 3600 (dilute sol.)
3100-3400 (conc. sol), 1690
λmax 285 (log ε 4.2)
δH 7.0 (2H d, J = 9 Hz)
7.8 (2H, d, J = 9 Hz)
9.8 (1H, s)
10.4 (1H, br s, exchanges in
D2O)
C; C7H6O2
νmax 3500-3000 (no change
on dilution), 1660
λmax 255 (log ε 4.0)
δH 7.0 (2H, m), 7.5 (2H, m)
9.9 (1H, s)
11.0 (1H, br s, exchanges in
D2O)
D; C19H16O3
νmax 3030, 1600, 1250, 750,
690
λmax 266 (log ε 3.4)
δH 6.6 (1H, s). 7.0-7.2 (15H,
m), no exchangeable protons
with D2O
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