Diprotonated Hydrogen Halides (H3X2+) and Gitonic Protio Methyl- and Dimethylhalonium Dications (CH3XH22+ and (CH3)2XH2+): Theoretical and Hydrogen−Deuterium Exchange Studies1

Abstract

Density functional theory (DFT) calculations at the B3LYP/6-31G** level were performed to investigate geometries and energies of a series of diprotonated hydrogen halides (H3X2+) and gitonic protio methyl- and dimethylhalonium dications (CH3XH22+ and (CH3)2XH2+). On the basis of computed energies, proton affinities and related thermodynamic parameters were also calculated. A hydrogen/deuterium exchange experiment of dimethylbromonium ion, (CH3)2Br+, with an excess of 4:1 DF/SbF5 superacid indicated lack of exchange at the methyl group supporting protonation of the nonbonded electron pair on the bromine leading to the involvement of gitonic protodimethylbromonium dication. A similar hydrogen/deuterium exchange experiment was also carried out on dimethylchloronium ion, (CH3)2Cl+.