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—(C6H4)—I—CtC—(CH2)4—Cl] and [4-NO2—(C6H4)—I—CtC—(CH2)4—Cl] asymmetric iodonium radicals was studiedtheoretically. Vertical electron affinities and DRC (dynamic reactioncoordinate) results were obtained and compared with experimentalevidence. In particular, the fluorine and nitro substituent groups wereselected because of (i) their opposite electron-withdrawing/electrondonatingeffects and (ii) experimental evidence that the grafting ability,in terms of alkynyl/aryl grafting ratio, increases with decreasingelectron-withdrawing nature of the para-position substituent on the phenyl ring. DRC results show that the dissociation dynamicsof the iodinealkynyl carbon bond, for the nitro-substituted iodonium, occurs on a longer time scale than that of the fluorinesubstitutediodonium. This finding is in agreement with the overall experimental results.