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 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

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

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

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.

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

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