A comprehensive N + scale of nucleophilicity in an equation including a Swain‐Scott response/selectivity parameter

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) 2 CH + 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  =  s E  ×  N + ″ +  c , where s E 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 sp 3 carbon, including S‐methyldibenzothiophenium triflate (reference substrate for the N T 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 s E . 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.