Transcript 24_15.html

Section 24.15
Spectroscopic Analysis of Phenols
Infrared Spectroscopy
infrared spectra of phenols combine features
of alcohols and aromatic compounds
O—H stretch analogous to alcohols near
3600 cm-1
C—O stretch at 1200-1250 cm-1
Figure 24.3: Infrared Spectrum of p-Cresol
CH3
C—H
OH
C—O
O—H
3500
3000
2500
2000
1500
1000
Wave number, cm-1
Francis A. Carey, Organic Chemistry, Fourth Edition. Copyright © 2000 The McGraw-Hill Companies, Inc. All rights reserved.
500
1H
NMR
Hydroxyl proton of OH group lies between alcohols
and carboxylic acids; range is ca. d 4-12 ppm
(depends on concentration). For p-cresol the OH
proton appears at d 5.1 ppm (Figure 24.4).
H
H
CH3
HO
H
H
Figure 24.4 (page 961)
H
H
HO
CH3
H
10.0
9.0
8.0
7.0
6.0
H
5.0
4.0
3.0
Chemical shift (d, ppm)
2.0
1.0
0
13C
NMR
OH
155.1
112..3
116.1
139.8
129.4
121.7
CH3 21.3
Oxygen of hydroxyl group deshields carbon
to which it is directly attached.
The most shielded carbons of the ring are those that
are ortho and para to the oxygen.
UV-VIS
Oxygen substitution on ring shifts lmax to longer
wavelength; effect is greater in phenoxide ion.
OH
O
lmax
lmax
lmax
204 nm
210 nm
235 nm
256 nm
270 nm
287 nm
–
Mass Spectrometry
Prominent peak for molecular ion. Most intense
peak in phenol is for molecular ion.
•+
OH
••
m/z 94