PREDICTION OF RATE CONSTANTS FOR CYANOHYDRIN FORMATION USING EQUILIBRIUM-CONSTANTS AND DISTORTION ENERGIES

Rate constants for cyanohydrin formation in aqueous solution can be pr edicted, with no use of kinetics information, by the application of a simple model requiring only equilibrium constants and distortion energ ies for the species involved in the reaction. The detailed model for c yanohydrin formation involves two reaction coordinates: C-C bond forma tion, which would lead to a cyanohydrin with an orthogonal geometry, a nd conversion of the carbonyl center from sp(2) to sp(3). Allowance mu st be made for the necessary desolvation of cyanide ion before C-C bon d formation begins and for the initial partial desolvation of the newl y formed cyanohydrin anion. The energies of the ''corner intermediates '' can be calculated, and then the rest of the surface can be deduced using an assumed interpolation formula. With distortion energies deriv ed from semiempirical or ab initio molecular orbital calculations and overall energy changes based on experimental equilibrium constants, an d with the assumption of a quadratic dependence of energy on reaction coordinates, the Literature data for rate constants for cyanohydrin fo rmation in solution can be matched for a representative selection of c ompounds spanning the reactivity range which has been studied.