ALPHA-EFFECT IN MENSCHUTKIN ALKYLATIONS

The Menschutkin-type alkylation of substituted N-methylanilines with methyl arenesulfonates is compared to the same reaction with substituted N-phenylhydroxylamines. The alpha-effects are small but measurable. The Hammett rho parameters are not useful in this reaction series as an index of transition-state character. The use of beta1g(Me) parameters along with beta(nuc) values allows the transition states to be placed on the energy surface. The pattern is that the alpha-nucleophiles form tighter transition states than the normal nucleophiles. The size of the alpha-effect is related to the ionization potentials (IPs) computed by the AM1 Hamiltonian for a wide variety of reactions showing the alpha-effect. The larger alpha-effects depend more greatly on the IP.