Abstract

Anomalous (reverse) substituent-induced 13C nuclear magnetic resonance chemical shifts at the carboxyl carbon (δco) in meta-substituted benzoic acids have been studied for 11 substituents having varying electronic effects in 4 aprotic (nonhydroxylic) solvents of varying polarity by employing different dual substituent parameter models. The regression results for apolar aprotic solvents provide a strong evidence for through space π-polarization mode of transmission of reverse meta-substituent effects on the carboxyl carbon in benzoic acids. The results for dipolar aprotic solvents indicate significant specific solvation of π-polarized forms of the acids. The study showed further that an apolar aprotic solvent has a distinct preference over a dipolar aprotic one for investigating intrinsic substituent effects on chemical shifts in aromatic molecules.

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