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Solvent sensitivity of ortho substituent effect on 13C NMR chemical shift of the carboxyl carbon (δco) in benzoic acid

✍ Scribed by Susanta K. Sen Gupta; Ruchi Shrivastava

Publisher
John Wiley and Sons
Year
2011
Tongue
English
Weight
190 KB
Volume
49
Category
Article
ISSN
0749-1581

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✦ Synopsis

A reverse ortho effect is observed for the ^13^ C NMR chemical shifts of the carboxyl carbon (δ~co~) in benzoic acids measured in aprotic solvents of varying polarity. The ortho effect on δ~co~ is best described by a combination of the reverse field and steric accelerating effects of the substituent in an 80: 20 pattern in apolar aprotic solvents and a 60: 40 pattern in dipolar aprotic ones. Interestingly, no good enough correlation was found between δ~co~ and log k~1~ of the acids measured in similar solvents. A critical analysis of the results clearly indicates the use of an apolar aprotic solvent and not a dipolar aprotic one as the solvent of choice for investigating intrinsic substituent effects on δ~c~ in an aromatic system. Copyright © 2011 John Wiley & Sons, Ltd.

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