Dissociation dynamics of asymmetric alkynyl(aryl)iodonium radicals: an ab initio DRC approach to predict the surface functionalization selectivity.

The dissociation process of neutral open-shell [4-F-(C(6)H(4))-I-C≡C-(CH(2))(4)-Cl] and [4-NO(2)-(C(6)H(4))-I-C≡C-(CH(2))(4)-Cl] asymmetric iodonium radicals was studied theoretically. Vertical electron affinities and DRC (dynamic reaction coordinate) results were obtained and compared with experimental evidence. In particular, the fluorine and nitro substituent groups were selected because of (i) their opposite electron-withdrawing/electron-donating effects and (ii) experimental evidence that the grafting ability, in terms of alkynyl/aryl grafting ratio, increases with decreasing electron-withdrawing nature of the para-position substituent on the phenyl ring. DRC results show that the dissociation dynamics of the iodine-alkynyl carbon bond, for the nitro-substituted iodonium, occurs on a longer time scale than that of the fluorine-substituted iodonium. This finding is in agreement with the overall experimental results.