The double hydrogen transfer in the 1-methoxy-2-propanol molecular ion: Loss of CH3CO by proton-transport catalysis

The previously proposed mechanism of the double hydrogen transfer in the molecular ion of 1-methoxy-2-propanol, which yields protonated dimethyl ether and a C2H3O radical [1], has been re-examined. To obtain a more refined picture of the structures of the intermediates and transition states as well as the energetics of this reaction, calculations using the CBS-QB3 model chemistry have been performed. In addition, collision-induced dissociative ionization (CIDI) experiments have been carried out which show that the eliminated C2H3O radical is solely the acetyl radical.Theory predicts that hydrogen-bridged radical cations (HBRCs) play a pivotal role in the reaction and that the lowest energy route involves loss of a CH3CO radical, by proton transport catalysis.Our mechanistic study also accounts for the minor H/D exchange observed in the DO-analogue of 1-methoxy-2-propanol and it proposes a revision of the energetics of the mechanisms of the earlier study [1].