1. Section 24.15 Spectroscopic Analysis of Phenols

2. Infrared Spectroscopy
infrared spectra of phenols combine features of alcohols and aromatic compounds
O—H stretch analogous to alcohols near cm-1
C—O stretch at cm-1

3. Figure 24.3: Infrared Spectrum of p-Cresol
CH3 OH
C—H
O—H
C—O
2000
3500
3000
2500
1000
1500
500
Wave number, cm-1
Francis A. Carey, Organic Chemistry, Fourth Edition. Copyright © 2000 The McGraw-Hill Companies, Inc. All rights reserved. 8

4. 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).
CH3 HO H

5. Figure 24.4 (page 961) H HO CH3 Chemical shift (d, ppm) 1 1.0 2.0 3.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
Chemical shift (d, ppm) 1

6. 13C NMR
CH3 OH
139.8
21.3
129.4
112..3
116.1
155.1
121.7
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.

7. UV-VIS
Oxygen substitution on ring shifts lmax to longer wavelength; effect is greater in phenoxide ion. – OH O
lmax
204 nm
256 nm
210 nm
270 nm
235 nm
287 nm

8. Mass Spectrometry
Prominent peak for molecular ion. Most intense peak in phenol is for molecular ion. OH •+ ••
m/z 94