Reactions of recoil tritium atoms with toluene and benzonitrile.

Recoil tritium reactions in the aromatic ring were investigated with toluene and benzonitrile in the moderator-free and the C6F6-moderated systems in terms of the intramolecular tritium distribution, the relative tritiation rate, and the isotope effect in toluene. The reactions free from hexafluorobenzene are in essential agreement with non-selective nature shown in hot atom reactions. The addition of the moderator to the systems changes more markedly the uniform labeling to o,p-orientation in toluene than in benzonitrile, and the 1.17 PhCH3/PhCN tritiation rate (in PhCH3-d8/PhCN, 0.942) to the 1.89 PhCH3/PhCN one (in PhCH3-d8/PhCN, 1.51) when the mole ratio of C6F6/substrate is about 100. These findings agree with the electrophilic nature of the tritium at lower energies. The H/D isotope effect in the moderated system is given as 1.89/1.51 or 1.25 and is substantially the same as that (1.24) in the moderator-free system.