Reactivity–selectivity relationships. Part 5. Effect of solvent ionizing power on the selectivity of diphenylmethyl derivatives

Abstract

The effect of solvent polarity on the selectivity of a series of substituted diphenylmethyl derivatives is investigated. The key result is that all substrates studied exhibit higher selectivity in solvents of higher polarity. Three possible explanations for this effect are proposed. (a) Greater stabilization of solvolytic intermediates in more polar solvents results in these species showing greater selectivity. (b) Increased solvent ionizing power results in greater dissociation to free ions which are intrinsically more selective. (c) The effect of an increase in solvent polarity on the nucleophilicity of ethanol and water may result in enhanced ethanol nucleophilicity. No clear differentiation between these three alternatives appears possible at the present time.