Sa. Shaffer et F. Turecek, HYDROGENTRIMETHYLAMMONIUM - A MARGINALLY STABLE HYPERVALENT RADICAL, Journal of the American Chemical Society, 116(19), 1994, pp. 8647-8653
Hydrogentrimethylammonium, (CH3)(3)NH., 1, and its deuterium-labeled i
sotopomers are generated by collisional neutralization with dimethyl d
isulfide of the corresponding stable cations and characterized by neut
ralization-reionization mass spectrometry and ab initio calculations.
Hypervalent radical 1 dissociates extensively by losses of hydrogen an
d methyl, which are calculated to be exothermic by 69 and 103 kJ mol(-
1), respectively. A small fraction (similar to 0.5%) of 1 is metastabl
e and survives for 3.7 mu s to be detected as stable ions after collis
ional reionization with oxygen. An unusual inverse deuterium isotope e
ffect on dissociations of 1 is found that stabilizes (CH3)(3)NH. and (
CHD2)(CH3)(2)NH. against (CH3)(3)ND.. MP2(FULL)/6-31+G(d) calculations
find a very shallow potential energy minimum for the (2)A(1) electron
ic ground state of 1, which is predicted to dissociate completely by l
oss of hydrogen. A potential energy barrier is found for the loss of m
ethyl from the (2)A(1) ground state of 1. The existence of metastable
1 and the methyl loss are explained by low-lying bound excited states
which are accessed on collisional neutralization.