A COMPARATIVE AM1 AND AB-INITIO STUDY OF THE INTRAMOLECULAR PROTON-TRANSFER IN TAUTOMERIC ORGANIC-COMPOUNDS

The proton-transfer barriers along the intramolecular hydrogen bond in a series of substituted salicylaldehyde anils were calculated using t he AM1 SCF semiempirical method. The reliability of this method for th e calculation of proton-transfer barriers was analyzed by the comparis on of AM1 barriers for a series of different tautomeric organic compou nds with those calculated using ab initio SCF and second-order perturb ation theory with extended basis sets. In general, the AM1 method syst ematically overestimates the barrier height. However, this error is ap proximately constant for given pairs of groups involved in the intramo lecular proton transfer. (C) 1996 John Wiley & Sons, Inc.