ON THE INTRAMOLECULAR PROTON TRANSFERS IN N,N'-BIS(SALICYLIDENE)-P-PHENYLENEDIAMINE

A molecular orbital quantum mechanical study of the two successive pro ton transfers in NHO hydrogen bonds in N,N'-bis (salicylidene)-p-pheny lenediamine has been performed, using the AM1 and PM3 Hamiltonians. We have observed that PM3 gives slightly higher barriers than AM1 but th e two semiempirical methods predict a practically negligible differenc e between the two intramolecular proton transfer processes. This resul t suggests that the two remarkably different activation energies found experimentally by Takeda et al., could be explained as a consequence of a typical non-Arrhenius behavior arising from proton tunnelling.