Quantum Tunneling in Hydride Transfer Reactions in Solutio

The secondary kinetic isotope effects for the hydride transfer reactions from aliphatic alcohols to four carbocations (NAD+ models) in acetonitrile were determined. The results suggest that the hydride transfer takes place by tunneling and that the rehybridizations of both donor and acceptor carbons lag behind the H-tunneling. This is quite contrary to the observations in alcohol dehydrogenases where the importance of enzyme motions in catalysis is manifested.