A COMPARATIVE-STUDY OF THE GAS-PHASE ACIDITIES OF ALIPHATIC-ALCOHOLS AND CARBOXYLIC-ACIDS FROM GENERALIZED VALENCE-BOND AND GENERALIZED MULTISTRUCTURAL CALCULATIONS

It is well-known that carboxylic acids and phenols are stronger acids than the corresponding aliphatic alcohols. The often accepted explanat ion is that carboxylate and phenoxy anions are stabilized by resonance . However, from a theoretical point of view, the inductive and resonan ce effects for these compounds have not yet been well quantified. Maki ng use of generalized multistructural (GMS) wave functions, we compute d the gasphase acidities of methanol, ethanol, formic acid, and acetic acid. It is shown that, in the absence of resonance, acetic acid is s lightly more acidic than ethanol and that the difference in acidity be tween formic acid and methanol is only half of the experimental value. Assuming that, in the absence of resonance, the difference in aciditi es can be attributed mainly to the inductive effect of the carbonyl gr oup, it can be shown that resonance is the dominant effect in determin ing the greater acidity of the carboxylic acids relative to the corres ponding aliphatic alcohols.