engleski

Gas-phase acidity of para-substituted benzoic acids - a triadic analysis of substituent effects

Deprotonation energies in vacuo of a large number of para-substituted benzoic acids encompassing a wide variety of substituents (F, Cl, Br, CH3, C(CH3)3, CH=CH2, C2H, CHO, COOH, CF3, BH2, B(CH3)2, NH2, N(CH3)2, OH, OCH3, SH, CN and NO2) are studied by reliable ab initio method. It is shown by using a triadic formula analysis that the enhanced acidity of these compounds is a consequence of the final state as a rule, i.e. it is a result of the greater stability of the conjugate bases. There are just a few exceptions to this rule involving C(CH3)3, OCH3, OH and SH substituent groups. In the latter two cases molecules deprotonate at the O and S substituent atoms, respectively. The ring-substituted pentacyano-derivative of benzoic acid is examined too. It is shown that it exhibits a highly pronounced acidity due to a strong anionic resonance effect in the resulting final state anion.

acidity; benzoic acid; deprotonation; substituent effects; triadic formula analysis

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