GAS-PHASE PROTON-TRANSFER REACTIONS BETWEEN ALKOXIDE ANIONS

Reaction efficiencies for proton transfer between alkoxide anions and neutral alcohols have been measured in an ion cyclotron resonance spectrometer, using a competition kinetics technique. The efficiencies for identity proton-transfer reactions are measurably less than 0.5, which is the simple statistical prediction for a thermoneutral reaction with no energetic barrier. In addition, the trend in reaction efficiencies for exothermic proton transfers is consistent with the presence of a substantial Marcus intrinsic barrier. An energetic barrier of this magnitude is not consistent with a surface which is believed to have little or no barrier. The results are consistent, however, with recent quasi-classical trajectory calculations which show that efficiencies for reactions on a barrierless surface can be slower than expected.