Section Spectroscopic Analysis of Carboxylic Acid Derivatives Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

C=O stretching frequency depends on whether the compound is an acyl chloride, anhydride, ester, or amide. Infrared Spectroscopy CH 3 CCl O CH 3 COCH 3 O CH 3 COCCH 3 OO CH 3 CNH 2 O 1822 cm and 1815 cm cm cm -1 C=O stretching frequency

Anhydrides have two peaks due to C=O stretching. One results from symmetrical stretching of the C=O unit, the other from an antisymmetrical stretch. Infrared Spectroscopy 1748 and 1815 cm -1 CH 3 COCCH 3 OO C=O stretching frequency

Nitriles are readily identified by absorption due to carbon-nitrogen triple bond stretching in the cm -1 region. Infrared Spectroscopy

1 H NMR readily distinguishes between isomeric esters of the type: 1 H NMR RCOR' O and R'COR O O C H is less shielded than O C C H

1 H NMR CH 3 COCH 2 CH 3 O and For example: CH 3 CH 2 COCH 3 O Both have a triplet-quartet pattern for an ethyl group and a methyl singlet. They can be identified, however, on the basis of chemical shifts.

13 C NMR Carbonyl carbon is at low field (  ppm), but not as deshielded as the carbonyl carbon of an aldehyde or ketone (  ppm). The carbon of a CN group appears near  120 ppm.

UV-VIS CH 3 CCl O 235 nm CH 3 COCH 3 O 225 nm CH 3 COCCH 3 OO 207 nm CH 3 CNH 2 O 214 nm n  * absorption: max

Most carboxylic acid derivatives give a prominent peak for an acylium ion derived by the fragmentation shown. Mass Spectrometry + RCX O RCX + O RC O + X

Amides, however, cleave in the direction that gives a nitrogen-stabilized cation. Mass Spectrometry + R RCNR' 2 O + RCNR' 2 O + O C NR' 2