alpha-effect with substituted N-methylbenzohydroxamates and substituted phenyldimethylsulfonium salts: Toward understanding of an intrinsic alpha-effect

Increasing electron demand in the reactions of G-NMBH anions with substituted phenyldimethylsulfonium ions decreases the alpha-effect for the methyl transfers toward 1.0 (zero effect). An extrapolation shows the possibility of an inverse effect (<1.0). The reactivity of G-NMBH anions correlates with SET parameters and with the known propensity of phenyldimethylsulfonium ions to accept a single electron into a sigma* C-S orbital concomitant with expulsion of a CH3 group. These correlations indicate inclusion of some SET character into the wavefunction of the S(N)2 transition state for these reactions, in agreement with the Shaik and Pross SCD model of the S(N)2 reaction.