Evaluation of AM1 Calculated Proton Affinities and Deprotonation Enthalpies

摘要

Proton affinities (PA) were calculated for 60 compounds and deprotonation ethalpies (DPE) for 80 compounds by using the AMI semiempirical molecular orbital model. With few exceptions, the errors in the calculated DPE's and PA's as well as in the calculated heats of formation of deprotonated and protonated species, are comparable with those in calculated heats of formation of neutral precursors. Intramolecular hydrogen bonding in bifunctional bases is also effectively reproduced. The main problems involve anions in which the charge is largely concentrated on one atom and anions formed by the deprotonation of oximes. Systematic errors are indicated in the extension of alkyl chains by addition of methene groups and in substitution of amine and hydroxyl hroups bonded to secondary or tertiary carbons in neutral molecules.