A New Interpretation of the Winstein Equation: Definition and Meaning of m Value

Abstract

A detailed analysis for the mechanism of unimolecular heterolysis is discussed in terms of a modified Grunwald-Winstein equation: log k = m₀Y + Δ, where m₀ is an intrinsic sensitivity of a given substrate determined for non-aqueous solvents and Δ is a correction term for hydrophobicity of the substrate defined as the difference in the logarithmic rate constant in pure water between the observed value and that predicted from a correlation line for non-aqueous solvents. Ionization with the transition state structure close to intimate ion pair, solvent-separated ion pair, and free ion is each characterized by an m₀ value of 1.00, 1.73, and 2.07, respectively, for the chloride solvolysis.