Electron distribution on an intramolecular hydrogen bond: A semiempirical AM1 study

Dipole moments of seven molecules were studied by AM1, each containing an intramolecular hydrogen bond between a hydroxyl group and a carbonyl or nitro group as hydrogen acceptors. The hydrogen bond causes two electron shifts: from H to O within the hydroxyl group and from C to O within the carbonyl group. The latter is accompanied by withdrawal of electrons from even more distant atoms. If the total electron density change is expressed as a vector, its direction is close to the direction of the O-H bond. This electron redistribution is in agreement with the previous, somewhat, puzzling experimental results. However, it differs from the commonly accepted picture according to which electron density changes on the hydrogen acceptor moiety are less important than those on the O-H bond.Dedicated to Professor Viktor Gutmann on the occasion of his 70th birthday.