Dissociation of Ionized 1,2-Ethanediol and 1,2-Propanediol: Proton-Transport Catalysis with Electron Transfer †

Ab initio molecular orbital (MO) calculations support the proposal that the key processes in the rearrangement of HOCH2CH2OH•+ and HOCH2CH(CH3)OH•+ (ionized 1,2-ethanediol and 1,2-propanediol) are sequential transfers of a proton and an electron taking place from one partner to the other in ion−dipole complexes rather than prompt hydrogen atom shifts taking place in distonic ions. Although the proposed distonic ions in the alternative mechanism (J. Am. Chem. Soc. 1992, 114, 2027) are thermodynamically remarkably stable species, a surprisingly large barrier exists for their interconversion by way of a 1,4-H atom shift. This large barrier results from significant distortion, from planarity, of the transition state. The rearrangement process of ionized 1,2-ethanediol and 1,2-propanediol can therefore best be described in terms of intramolecular catalysis (proton transport catalysis, Int. J. Mass Spectrom. Ion Processes 1992, 115, 95) in combination with an electron transfer taking place in intermediate ion−dipole complexes.