title: Solvent sensitivity of ortho substituent effect on 13C NMR chemical shift of the carboxyl carbon (δco) in benzoic acid.
abstract: 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.
authors: Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi-221005, India. sksbhuchem@yahoo.co.in
authors: Susanta K Sen
authors: SK
authors: Gupta
authors: Ruchi
authors: R
authors: Shrivastava
mesh_terms: D019817:Benzoic Acid / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D002247:Carbon Isotopes; D009682:Magnetic Resonance Spectroscopy / Q000592:standards; D015394:Molecular Structure; D012015:Reference Standards; D012997:Solvents / Q000737:chemistry
chemical_list: D002247:Carbon Isotopes; D012997:Solvents; D002244:Carbon; D019817:Benzoic Acid