The Formation of Protonated Dimethyl Ether from the Metastable Molecular Ions of 1-Methoxy-2-Propanol, CH 3 OCH 2 CH(OH)CH 3

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The unimolecular metastable decomposition of 1-methoxy-2-propanol, CH 3 OCH 2 CH(OH)CH 3 (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, CH 3 O + (H)CH 3 ] by the loss of a C 2 H 3 O 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, C 2 H 3 O. In the present study it is shown that more DHT mechanisms are operative, leading to the losses of isomeric C 2 H 3 O radicals. The results obtained are best explained by the formation of the key intermediate ion–molecule complexes [CH 3 OCH 3 +• , CH 3 CHO] and [CH 3 OCH 3 , CH 2 =C(H)OH +• ] following unimolecular metastable dissociation of the molecular ion. Subsequent hydrogen atom abstraction channels by CH 3 OCH 3 +• in the former complex and proton abstraction channels by CH 3 OCH 3 in the latter complex lead eventually to the formation of protonated dimethyl ether with m/z 47.