Abstract
A set of N+ nucleophilicity parameters (N+″) are reported for amines, carbanions and various other nucleophiles in methanol at 20 °C. N+″ = N″ +2.63, where N″ refers to logarithms of second‐order rate constants for reactions of the dimethylamino‐ benzhydrylium cation (dma)2CH+ with various nucleophiles in any solvent at 20 °C; as for other N+ parameters, N+″ = 4.75 for hydroxide in water. Logarithms of second‐order rate constants (log k) are correlated by a hybrid of Swain‐Scott and Ritchie (SSR) equations: log k = sE × N+″ + c, where sE is the response of the electrophile to changes in N+″ and c is a residual intercept term. Satisfactory results are obtained for some nucleophilic reactions at sp3 carbon, including S‐methyldibenzothiophenium triflate (reference substrate for the NT scale of solvent nucleophilicity), a methoxymethyl derivative and methyl p‐nitrobenzenesulfonate. Less satisfactory results are obtained for acetyl chloride. The results extend the scope of the hybrid SSR equation to nucleophilic substitutions and provide additional insights into the factors influencing sE. A previously published equation containing two response (s) parameters is shown to be less reliable, and an alternative is investigated. Copyright © 2012 John Wiley & Sons, Ltd.
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