|
Spectroscopic Analysis
|
Chapter 24:
Phenols
|
- IR - presence
of -OH and aromatic CC and CH
|
Absorbance (cm-1)
|
Interpretation
|
|
3600 (strong, broad)
|
OH stretch
|
|
> 3000
|
aromatic CH stretch
|
|
1600
|
CC stretch (pairs)
|
|
1200-1250
|
C-O stretch
|
- 1H
NMR -OH proton is more deshielded (higher ppm) in a phenol
than in an alcohol.
|
Resonance (ppm)
|
Interpretation
|
|
4-12 (exchangeable)
|
-OH proton
|
|
7-8
|
aromatic protons,
Ar-H
|
(exchangeable means that
the peak "disappears" when shaken with D2O)
- 13C
NMR
C-O carbon in the aromatic ring is deshielded by 25 ppm vs the aromatic
C-H carbons
Most shielded C-H carbons of ring are located ortho and para to
the OH (recall resonance forms)
-
UV-VIS
-OH group affects benzene chromophore by shifting lmax to
longer wavelengths.
The effect is very large in basic solution as a result of OH conversion to O-.
- Mass
Spectrometry
Peak for the molecular ion, M+, is usually prominent