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 tha t the key processes in the rearrangement of HOCH2CH2OH.+ and HOCH2CH(C H3)OH.+ (ionized 1,2-ethanediol and 1,2-propanediol) are sequential tr ansfers of a proton and an electron taking place from one partner to t he other in ion-dipole complexes rather than prompt hydrogen atom shif ts taking place in distonic ions. Although the proposed distonic ions in the alternative mechanism (J. Am. Chem. Sec. 1992, 114, 2027) are t hermodynamically remarkably stable species, a surprisingly large barri er 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-ethane diol and 1,2-propanediol can therefore best be described in terms of i ntramolecular catalysis (proton transport catalysis, Int. J. Mass Spec trom. Ion Processes 1992, 115, 95) in combination with an electron tra nsfer taking place in intermediate ion-dipole complexes.