N
X
C
Hal
O
N
S
P Si
Natural
Products
Solvents
C
C
C
C C
C
211
5.8 Alcohols, Ethers, and Related Compounds
211
5.8 Alcohols, Ethers, and Related Compounds
5.8.1 Alcohols
1 H Chemical Shifts and Coupling Constants (δ in ppm, J in Hz)
Aliphatic and alicyclic alcohols:
δ OH = 0.5–3.0 (in DMSO: 4–6) ppm
Phenols:
δ OH = 4.0–8.0 (in DMSO: 8–12) ppm
Hydrogen bonds strongly deshield hydroxyl protons. The position of the signal may
depend heavily on the experimental conditions including the concentration of the
sample. If a compound contains several kinds of hydroxyl protons (–OH, –COOH,
H 2 O), in general only one signal at an average position is seen because of rapid
exchange. In dimethyl sulfoxide (DMSO) as solvent, this exchange in most cases
is so slow that isolated signals are obtained. In this case, the chemical shifts of
hydroxyl protons are characteristic. However, if the sample contains strong acids or
amine bases, the exchange rate increases and, also in DMSO, a single signal at an
average position is observed. Frequently, intermediate exchange rates lead to very
broad signals extending over several ppm and, therefore, sometimes not discernible
in routine spectra.
As a consequence of fast intermolecular exchange of the hydroxyl protons, their
coupling with the protons on the adjacent carbon atoms is usually not observed.
However, in very pure (acid-free) solutions or in DMSO, the exchange is sufficiently slow so that the H–O–C–H couplings become visible. Their dependence on
the conformation is analogous to that shown by the H–C–C–H couplings (Chapter
5.1.2). In case of fast rotation: 3 J HOCH ≈ 5 Hz. In cyclohexanols, the vicinal coupling constants for axial hydroxyl protons (3.0–4.2 Hz) are lower than those of
equatorial ones (4.2–5.7 Hz).
CH 3 OH
OH
a
a
c
b
OH
a
c
b
b
d
CDCl 3 DMSO D 2 O
a 1.13
4.05
b 3.49
3.17
3.34
3 J ab 5.2
CDCl 3 DMSO D 2 O
a 1.51
4.31
b 3.71
3.44
3.65
c 1.24
1.06
1.17
3 J ab 4.8
3 J bc 6.9
CDCl 3 DMSO D 2 O
a 1.51
4.31
b 3.59
3.34
3.61
c 1.59
1.42
1.57
d 0.94
0.84
0.89
X
C
Hal
O
N
S
P Si
Natural
Products
Solvents
C
C
C
C C
C
211
5.8 Alcohols, Ethers, and Related Compounds
211
5.8 Alcohols, Ethers, and Related Compounds
5.8.1 Alcohols
1 H Chemical Shifts and Coupling Constants (δ in ppm, J in Hz)
Aliphatic and alicyclic alcohols:
δ OH = 0.5–3.0 (in DMSO: 4–6) ppm
Phenols:
δ OH = 4.0–8.0 (in DMSO: 8–12) ppm
Hydrogen bonds strongly deshield hydroxyl protons. The position of the signal may
depend heavily on the experimental conditions including the concentration of the
sample. If a compound contains several kinds of hydroxyl protons (–OH, –COOH,
H 2 O), in general only one signal at an average position is seen because of rapid
exchange. In dimethyl sulfoxide (DMSO) as solvent, this exchange in most cases
is so slow that isolated signals are obtained. In this case, the chemical shifts of
hydroxyl protons are characteristic. However, if the sample contains strong acids or
amine bases, the exchange rate increases and, also in DMSO, a single signal at an
average position is observed. Frequently, intermediate exchange rates lead to very
broad signals extending over several ppm and, therefore, sometimes not discernible
in routine spectra.
As a consequence of fast intermolecular exchange of the hydroxyl protons, their
coupling with the protons on the adjacent carbon atoms is usually not observed.
However, in very pure (acid-free) solutions or in DMSO, the exchange is sufficiently slow so that the H–O–C–H couplings become visible. Their dependence on
the conformation is analogous to that shown by the H–C–C–H couplings (Chapter
5.1.2). In case of fast rotation: 3 J HOCH ≈ 5 Hz. In cyclohexanols, the vicinal coupling constants for axial hydroxyl protons (3.0–4.2 Hz) are lower than those of
equatorial ones (4.2–5.7 Hz).
CH 3 OH
OH
a
a
c
b
OH
a
c
b
b
d
CDCl 3 DMSO D 2 O
a 1.13
4.05
b 3.49
3.17
3.34
3 J ab 5.2
CDCl 3 DMSO D 2 O
a 1.51
4.31
b 3.71
3.44
3.65
c 1.24
1.06
1.17
3 J ab 4.8
3 J bc 6.9
CDCl 3 DMSO D 2 O
a 1.51
4.31
b 3.59
3.34
3.61
c 1.59
1.42
1.57
d 0.94
0.84
0.89