THE REACTIVE NATURE OF ALPHA-AMMONIUM DISTONIC RADICAL CATIONS

Tbe enhanced reactivity of alpha-ammonium distonic radical cations has been shown to derive from a combination of thermodynamic and polar fa ctors. Ab initio calculations demonstrate that an alpha-ammonio substi tuent destabilizes an alkyl radical, hence increasing the exothermicit y of its C-C bond-forming reactions. Secondly, a Hammett study involvi ng cyclization of such radicals has confirmed their electrophilic natu re. In this study, a good correlation between the log k(rel)'s for cyc lizations of a series of p-substituted N-dimethyl-N-(5-aryl-4-pentenyl )methanaminium-1-yl radicals and the sigma(+) values of the substituen ts was obtained (p(+) = -0.29, <r> = 0.954). (C) 1997 Elsevier Science Ltd.