MECHANISTIC VIEWS ON AROMATIC-SUBSTITUTION REACTIONS BY GASEOUS CATIONS

Recent advances in the understanding of the gas-phase reaction of arom atics with cationic electrophiles in a thermally equilibrated domain a re described. The overall substitution reaction is analyzed in terms o f its elementary steps. Their contribution to the overall reactivity p attern is dissected by the use of selected systems, which allowed one to highlight the kinetic role of single elementary events. Mechanistic studies have focused on the structure and reactivity of covalent and non-covalent ionic intermediates, which display a rich chemistry and p rovide benchmark reactivity models. Particular interest has been devot ed to proton transfer reactions, which may occur in either an intra- o r inter-molecular fashion in arenium intermediates. A quantitative stu dy of their rates and associated kinetic isotope effects is reported. (C) 1997 John Wiley & Sons, Inc.