Aromatic substitution in the gas phase. Ambident behavior of halo- and dihalobenzenes toward D2T+. Tritiodeprotonation vs. tritiodehalogenation

The gas-phase electrophilic attack of radiolytically formed D2T+ ions on halo- and dihalobenzenes was investigated in homogeneous systems formed by a large excess (760 torr) of D2 labeled with DT and contg. at low concns. (∼1 torr) the arom. substrate and a thermal radical scavenger. Tritiodeprotonation, to give the tritiated substrate or its isomers, and tritiodehalogenation occurred. The relative rate of the 2 competing reactions was detd. by the nature of the halogen atom(s) contained in the substrate; the extent of dehalogenation increased in the order Br ≤ Cl << F. Tritiodeprotonation involved the attack of D2T+ on the arom. π system. Tritiodehalogenation involved the attack of the gaseous electrophile to the n center(s) of the substrate. These channel mechanisms were independently supported by ion cyclotron resonance and chem. ionization mass spectrometric data. The results obtained with different gaseous electrophiles and in related soln. reactions were discussed.