Diprotonated hydrogen halides (H3X2+) and gitonic protio methyl and dimethylhalonium dications (CH3XH22+ and (CH3)(2)XH2+): Theoretical and hydrogen-deuterium exchange studies

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