The formation of protonated dimethyl ether from the metastable molecular ions of 1-methoxy-2-propanol, CH

₃OCH₂CH(OH)CH₃

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Eur. J. Mass Spectrom. 7, 47 - 53 (2001)

The formation of protonated dimethyl ether from the metastable molecular ions of 1-methoxy-2-propanol, CH₃OCH₂CH(OH)CH₃

Satoshi Nakajima, Tatsuki Asakawa, Osamu Sekiguchi and Susumu Tajima ^*
Chemistry and Materials Science, Gunma National College of Technology, Maebashi, Gunma , Japan
Nico M.M. Nibbering ^*
Physical Chemistry, Laser Center, Division Chemistry, Faculty of Exact Sciences, Free University, De Boelellan 1083, 1081 HV Amsterdam, The Netherlands

ABSTRACT:

The unimolecular metastable decomposition of 1-methoxy-2-propanol, CH₃OCH₂CH(OH)CH₃ (mol. wt. 90) induced by electron ionization, has been investigated by use of mass-analyzed ion kinetic energy (MIKE) spectrometry and D-labeling in conjunction with thermochemical data. In the metastable time window, the molecular ions decompose almost exclusively into ions at m/z 47 [i.e. protonated dimethyl ether, CH₃O⁺(H)CH₃] by the loss of a C₂H₃O radical species following a double hydrogen atom transfer (DHT). Until now, only one DHT mechanism has been proposed, involving and accounting for the loss of an acetyl radical, C₂H₃O. In the present study it is shown that more DHT mechanisms are operative, leading to the losses of isomeric C₂H₃O radicals. The results obtained are best explained by the formation of the key intermediate ionmolecule complexes [CH₃OCH₃^+", CH₃CHO] and [CH₃OCH₃, CH₂=C(H)OH^+"] following unimolecular metastable dissociation of the molecular ion. Subsequent hydrogen atom abstraction channels by CH₃OCH₃^+" in the former complex and proton abstraction channels by CH₃OCH₃ in the latter complex lead eventually to the formation of protonated dimethyl ether with m/z 47.

Keywords: 1-methoxy-2-propanol, double hydrogen atom transfer (DHT), D-labeling, MIKE spectrometry, ionmolecule complexes

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