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■ Substituent Effects on Proton Affinities: Through Bonds or through Space Mechanism?

Javier Catalán, Pilar Pérez, and José Elguero

*Departamento de Química Orgánica, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049-Madrid, Spain

Abstract

INDO calculations of the protonation energies and lone pair orbital energies of twenty pyrazoles and twenty imidazoles have been carried out in order to ascertain the mechanism of the substituent effect. Methyl, cyano, fluoro, amino, and nitro substituents have been examined. The last one shows a special behaviour. The importance to optimize the geometry and the reasons for the anomaly shown by the nitro derivatives are discussed.