A THEORETICAL-STUDY OF PROTON-TRANSFER IN [2,2'-BIPYRIDYL]-3,3'-DIOL

Thermochemical and mechanistic aspects of tautomerization resulting from proton transfer in [2,2′-bipyridyl]-3,3′-diol have been investigated by ab initio computations. From a classical point of view, complete characterization of energy minima and first-order saddle points indicates that proton transfer occurs through a step-wise mechanism. However, the di-enol form is sufficiently more stable than the other two tautomeric forms (keto-enol and di-keto) to be the only experimentally detectable species. Furthermore, the reverse activation barrier for the first step is so low that no vibrational level is completely localized in the region separating the two saddle points. As a consequence the keto-enol form lacks individuality from a quantum-mechanical point of view.