Analysis of the Gas Phase Acidity of Substituted Benzoic Acids Using Density Functional Concepts.

A theoretical study of the effect of the substituent Z on the gas phase acidity of substituted benzoic acids ZC6H4COOH in terms of density functional theory descriptors (chemical potential, softness and Fukui function) is presented. The calculated gas phase ΔacidG° values obtained were close to the experimental ones reported in the literature. The good relationship between the ΔacidG° values and the electronegativity of ZC6H4COOH and its fragments, suggested a better importance of the inductive than polarizability contributions. The balance of inductive and resonance contributions of the substituent in the acidity of substituted benzoic acids showed that the highest inductive and resonance effects were for the -SO2CF3 and -NH2 substituents in the para- and ortho-position, respectively. The Fukui function confirmed that the electron-releasing substituent attached to the phenyl ring of benzoic acid decreased the acidity in the trend ortho > meta > para, and the electron-withdrawing substituent increased the acidity in the trend ortho < meta < para.

Hyperconjugation enhances electrophilic addition to monocyclic monoterpenes: a Fukui function perspective.

The local and condensed Fukui functions as well as the principle of hard and soft acids and bases were used to study the addition of free radicals to the exocyclic and endocyclic double bonds of seven monocyclic monoterpenes of formula C10H16. The results obtained showed that, in general, the most reactive double bond was the one with the most substituents on the double-bonded carbon atoms, and that the reaction of a double bond with an electrophile is a soft-soft interaction. The effects of substituents on the double-bonded carbon atoms and the stabilization of the monoterpenes were interpreted by invoking hyperconjugated structures, which led us to propose a simple rule: the larger the value of the Fukui function for the double bond, the greater the hyperconjugative stabilization and the susceptibility of the double bond to electrophilic attack. In general, our results are in good accordance with relevant experimental and theoretical results published in the literature. Graphical abstract The specific electrophilic addition to monocyclic monoterpenes.