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Title: Quantification of substituent effects using molecular electrostatic potentials: Additive nature and proximity effects
Authors: Sayyed, F B
Suresh, C H
Keywords: Nuclear magnetic resonance
Hammett sigma constants
Benzoic -acids
Steric Inhibition
Chemometric analysis
Aromatic ring
Issue Date: 2009
Publisher: Royal Society of Chemistry
Citation: New Journal of Chemistry 33(12):2465-2471;2009
Abstract: Several ortho, meta, and para substituted benzoic acids have been studied to quantify the substituent effects by analysing subtle variations in the molecular electrostatic potential minimum (V(min)) at the response site of the carboxylic acid moiety using density functional theory. For the first time, the ortho substituent effect is separated into contributions from electronic and proximity effects. A molecular fragment approach in conjunction with a rotation experiment on the COOH moiety of benzoic acid was used to quantify the proximity effects. The quantified proximity effect is in accord with previously proposed steric parameters. The proximity effect-corrected V(min) of ortho systems showed excellent linear correlations to both V(min) of para and meta systems which enabled the computation of the meta : para, ortho : para and meta : ortho electronic effect ratios yielding respective values of 1 : 1.108, 1 : 1.042 and 1 : 1.047. The additive nature of the substituent effects was also tested using the V(min) computation on multiply-substituted benzoic acids. It is found that the total substituent effect is approximately 86.3% of the sum of the individual contributions which was in contrast to a value of 98.5% observed in aliphatic systems
ISSN: 1144-0546
Appears in Collections:2009

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