Nuclear Magnetic Resonance and 1 H Nmr Essay

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Experiment 2

STRUCTURE ELUCIDATION (MS, IR, 1H NMR 13C NMR)
Demonstrators sheet Compound 1
1

H NMR

2.2, 6H, s OR 2.25, 6H, s
13

6.9, 2H, s

2.2, 6H, s OR 2.25, 6H, s Chromophore

C NMR

20 OR 16

133 OR 134

127

133 OR 134

20 OR 16

Compound 2 IR & 1H NMR
1686 cm-1 1.75, 2H, tq (apparent sextet) CH2 splits signal into t CH3 splits signal into q 1.0, 3H, t CH2 splits signal into t 7.4-8.05, 5H, m 2.9, 2H, t CH2 splits signal into t Chromophore O

O

13

C NMR
137 18 O 128 OR 129 128 OR 129 133 40 201 13

Compound 3 IR & 1H NMR
1750 cm-1

4.1, 2H, q CH3 splits signal into q 1.2, 3H, t CH2 splits signal into t O

O

O 2.2, 3H, s

3.25, 2H, s
13

C NMR
59.2 O 13.6 O 207.1 172.0 46.6 O 24.2

Compound 4 IR & 1H NMR
1.25, 6H, t CH2 splits signal into t

1735 cm-1

O O O
2.6, 4H, s

O

4.15, 4H, q CH3 splits signal into q

13

C NMR
13

173 O O O 28 60 O

Compound 5
1

H NMR
3.2, 6H, s

O

O

1.35, 6H, s
13

C NMR
48 100 O O

24

Compound 6 Using the material covered in CHEM2210 you should be able to narrow the structure down to either 2-furoic acid or 3-furoic acid:
O H H
3 4 5 2

OH O H O

OH
3 4

H
2

O
5

H

H

2-furoic acid

3-furoic acid

To distinguish between these two possibilities requires detailed knowledge of coupling constants between protons attached to the furan ring:
1-2 Hz H 3-4 Hz H H
3 4 5 2

O H 1-2 Hz

0-1 Hz

From the coupling constant information, you can see that a relatively large coupling (3-4 Hz) exists between the protons at 3 and 4 positions of the furan ring. If you closely examine the coupling constants from the spectrum, you can see that there is one coupling constant significantly larger than the others, so the compound must be 2-furoic acid. If the compound was 3-furoic acid, all couplings would be small (less than 2 Hz). Consideration of coupling constant information allows the following assignment of the 1H NMR spectrum to be made: IR & 1H NMR
1695 cm-1 7.34, 1H, dd HA splits signal into d HB splits signal into d O HC O HB 6.58, 1H, dd HA splits signal into d HC splits signal into d HA 7.66, 1H, dd HB splits signal into d HC splits signal into d OH 2200-3400 cm-1 12.3, 1H, s

13

C NMR
O 143 111, 120 O 148 OH 163

To assign the 13C NMR spectrum, the CO2H carbon is easy (based on chemical shift). The quaternary carbon is most likely the carbon with the smallest signal, and the other carbon in the ring adjacent to O is most likely the remaining carbon with a relatively downfield
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