Hypervalent ammonium radicals. Effects of alkyl groups and aromatic substituents

Neutralization by collisional electron transfer of gaseous benzylalkylammonium ions produces transient hypervalent radicals whose dissociations depend on the substituents in the aromatic ring and at the amine nitrogen atom. Benzylammonium radical, C6H5CH2NH3 ., dissociates mainly by N-H bond cleavage to give benzylamine. Dissociation of the CH2-N bond to benzyl radical and ammonia is less abundant. Benzylmethylammonium, C6H5CH2NH2CH3 ., dissociates by CH2-N, N-CH3, and N-H bond cleavages to give methylamine, benzyl radical, benzylamine, and N-methylbenzylamine. Benzyldimethylammonium, C6H5CH2NH(CH3)(2) . undergoes loss of dimethylamine and hydrogen, while the loss of methyl is less important. (2,3,4,5,6-Pentafluorobenzyl)dimethylammonium radical, C6F5CH2NH(CH3)(2) ., dissociates mainly by fission of the pentafluorophenyl ring to give CnFm fragments with CF . as the dominating product, while bend dissociations at the hypervalent nitrogen atom are less important. The relative stabilities of pentafluorobenzyl and tropyl cations and radicals are assessed by ab initio calculations. (3,5-Dinitrobenzyl)dimethylammonium radical, (NO2)(2)C6H3CH2NH(CH3)(2) . undergoes competitive losses of hydrogen and NO and intramolecular proton transfer onto the dinitrophenyl ring. Mechanisms for these reactions are suggested involving dissociative electron attachment at the aromatic ring and formation of hypervalent ammonium radicals and zwitterionic intermediates.