HYPERVALENT AMMONIUM RADICALS - EFFECTS OF ALKYL-GROUPS AND AROMATIC SUBSTITUENTS

Neutralization by collisional electron transfer of gaseous benzylalkyl ammonium ions produces transient hypervalent radicals whose dissociati ons depend on the substituents in the aromatic ring and at the amine n itrogen atom. Benzylammonium radical, C6H5CH2NH3 ., dissociates mainly by N-H bond cleavage to give benzylamine. Dissociation of the CH2-N b ond to benzyl radical and ammonia is less abundant. Benzylmethylammoni um, C6H5CH2NH2CH3 ., dissociates by CH2-N, N-CH3, and N-H bond cleavag es to give methylamine, benzyl radical, benzylamine, and N-methylbenzy lamine. 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 d issociations at the hypervalent nitrogen atom are less important. The relative stabilities of pentafluorobenzyl and tropyl cations and radic als are assessed by ab initio calculations. (3,5-Dinitrobenzyl)dimethy lammonium radical, (NO2)(2)C6H3CH2NH(CH3)(2) . undergoes competitive l osses of hydrogen and NO and intramolecular proton transfer onto the d initrophenyl ring. Mechanisms for these reactions are suggested involv ing dissociative electron attachment at the aromatic ring and formatio n of hypervalent ammonium radicals and zwitterionic intermediates.