The [+CH2OH, H2O] and [+CH2OH, 2H(2)O] solvated ions

The reaction of CH3CH2OH.+ with (H2O)-O-18 in the gas phase has been studied by FT-ICR spectroscopy. The main reaction yields the product ion [CH2O ... H+...(OH2)-O-18]. This ion slowly exchanges its second oxygen with (H2O)-O-18. Two possible channels for this reaction will be successively discussed. (i) In the first, the permutation of both oxygens take place within [CH2O ... H+...(OH2)-O-18], leading to [(CH2O)-O-18 ... H+... OH2]. This last ion can in turn undergo a ligand exchange with (H2O)-O-18, yielding [(CH2O)-O-18 ... H+...(OH2)-O-18]. In this first hypothesis, a second molecule of water intervenes after an unimolecular rearrangmeent process with the [CH2O ... H+...(OH2)-O-18] ion. (ii) Converseley, a second possible mechanism involves as a first step a nucleophilic attack of (H2O)-O-18 at the carbon atom. In that case the rearrangement takes place within a [+CH2OH, 2H(2)O] solvated ion. It will be shown that the first process is strongly endothermic and therefore less likely than the second, in which the solvation effect strongly decreases the energy of the intermediate, and where H2O catalyses migrations of H. (C) 1997 Elsevier Science B.V.