1,3-DIPOLAR CYCLOADDITION REACTIONS - A DFT AND HSAB PRINCIPLE THEORETICAL-MODEL

The hard and soft acids and bases principle is used together with the condensed fukui function to analyze the regioselectivity and reactivit y of two model 1,3-dipolar cycloaddition reactions. Results obtained f or benzonitrile oxide with vinyl p-nitrobenzoate or 1-acetyl vinyl p-n itrobenzoate illustrate the value of these concepts to describe their inherent reactivity. The calculations of the interaction energy by den sity functional theory using a perturbative, orbital independent metho d suggest the specific direction of the electronic process at each of the reaction sites. The electrophilic nature of the 1,3-dipole and the nucleophilic nature of the two dipolarophiles was determined by this model. The partitioning of the interaction energy in a term resulting from the chemical potential equalization principle at constant externa l potential and a term resulting from the maximum hardness principle a t constant chemical potential show that the former term, arising from the charge-transfer process, contributes to a lesser extent than the t erm arising from the reshuffling of the charge distribution. The use o f density functional theory concepts and the hard and soft acids and b ases principle is a promising alternative to frontier orbital theory.