USING THEORETICAL DESCRIPTORS IN QUANTITATIVE STRUCTURE-PROPERTY RELATIONSHIPS - 3-CARBOXYBENZISOXAZOLE DECARBOXYLATION KINETICS

The decarboxylation rate of 3-carboxybenzisoxazoles depends on the substituent and strongly on the solvent. Solvent dependence explanation has been based on solvent donor hydrogen bond acidity, ion pairing and dispersive interactions. Recently, to help sort the solvent effects, the empirical, Kamlet-Taft-Abraham solvatochromic parameter set has been used as a probe in a multilinear correlation analysis based on the linear solvation energy relationship (LSER) model. This paper extends the LSER work with a theoretical, computational set of molecular parameters to analyse the rate data. Good correlations and physical interpretations result and agree with empirical observations and LSER correlations. These imply a rate decrease with solvent donor hydrogen bond acidity (HBA) and increase with acceptor hydrogen bond basicity (HBB). Mechanistic interpretation can involve the way charge delocalization on the carboxylate is effected by solvent HBA interaction and by ion pairing which is, in turn, effected by solvent HBB.