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

作者：Bentley T William^*

来源：Journal of Physical Organic Chemistry, 2013, 26(12): 977-982.

DOI：10.1002/poc.3067

• N+ nucleophilicity scale
• Swain-Scott equation
• S(N)2 reactions
• kinetics

A set of N+ nucleophilicity parameters (N+) are reported for amines, carbanions and various other nucleophiles in methanol at 20 degrees 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 degrees 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)xN(+)+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.

• 出版日期2013-12