Influence of solvent and cation on the properties of oxygen-containing organic anions. Part 1. Regioselectivity of methylation of acetophenone enolate

Abstract

Acetophenone enolates of lithium, sodium, and potassium were methylated with dimethyl sulphate in 14 aprotic solvents. Linear correlations of the logarithm of the molar ratio of O-methylation versus C-methylation products log(Q_O/Q_C) with solvent polarity and Lewis basicity parameters and either the ionic radius r_M or the reciprocal of the ionic volume (r^–3_M) of the metal were found. The results were interpreted with the help of HOMO energies of the enolates, their polarity index q_O/q_C(excess of negative charge densities on O and α-C), and frontier orbital index c²_C/c²_o, as a function of the correcting parameter δ_O in HMO calculations which characterizes the action of the cation field upon the electron distribution in the enolate.