REACTIONS BETWEEN PROTONATED AND NEUTRAL METHANOL IN THE GAS-PHASE - AN AB-INITIO MOLECULAR-ORBITAL STUDY

Ab initio molecular orbital calculations at the MP2/6-31G/MP2/6-31G* + ZPE level have been performed in order to explore the reaction betwe en CH3OH2+ and CH3OH. The detailed mechanism of proton transfer, CH3OH 2+ + CH3OH --> CH3OH + CH3OH2+, and of cationic nucleophilic substitut ion CH3OH2+ + CH3OH --> (CH3)(2)OH+ + H2O has been investigated. The f ormer reaction involves a symmetric proton bound dimer, I, [CH3OHa---H -b---HcOCH3](+), in which exchange of the three hydrogens H-a,H-b,H-c is allowed (critical energy ca, 50 kJ mol(-1)). The nucleophilic subst itution process involves two ion neutral complexes II, [CH3O(H)---CH3O H2](+), and III, [CH3OHC(H-3)---OH2](+), only weakly stable toward iso merization. The methyl cation transfer II --> III is calculated to req uire 28 kJ mol(-1). The proposed reaction profile supports and complet es the previous theoretical and experimental studies on this system, ( C) 1997 John Wiley & Sons, Ltd.