STRUCTURAL ASPECTS OF trans–cis ISOMERIZATION OF AZOBENZENE, 4,4′-AZOPYRIDINE, AND AZOXYBENZENE

Processes of trans–cis isomerization of azobenzene (AZB), 4,4′-azopyridine (AZP), and azoxybenzene (AZOB) are studied using quantum chemical calculations at the DFT/B3LYP/cc-pvTZ level of theory. The chosen objects can serve as reference points when studying intramolecular rearrangements of numerous compounds containing an azo group and an azoxy bridging group. Geometric and electronic characteristics of trans and cis isomers AZB and AZP and four AZOB isomers, as well as transition states (TSs) between them, are determined. It is established that two AZOB isomers containing a semi-polar bond N→O have a significantly lower energy than two isomers with a cyclic NON bridging group. The transition between the low-energy trans–cis isomers proceeds via a TS while preserving the N→O bond so that the oxygen atom does not migrate between the nitrogen atoms. The NBO analysis of the electronic structure is performed, the factors stabilizing the obtained geometric configurations of all isomers and transition states are determined.