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Solvent sensitivity of ortho substituent effect on 13 C NMR chemical shift of the carboxyl carbon ( δ co ) in benzoic acid
Author(s) -
Sen Gupta Susanta K.,
Shrivastava Ruchi
Publication year - 2011
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.2802
Subject(s) - chemistry , substituent , steric effects , solvent , solvent effects , benzoic acid , chemical shift , carbon 13 nmr , solvent polarity , organic chemistry , dipole , medicinal chemistry , computational chemistry
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.