Electronic structure of 1,4-dihydro-1,2,4,5-tetrazines and of related 1,4-dihydroaromatic compounds
1,4-Dihydro-1,2,4,5-tetrazine (1) and its 1,4-dimethyl(2) and 1,4-bis(trimethylsilyl)(3) derivative have been studied by photoelectron spectroscopy and cyclic voltammetry. The compounds are electron-rich, albeit not as much as the corresponding 1,4-dihydropyrazines. Electrochemical data illustrate the stability of the 1,4-dihydro form in the tetrazine system and of the radical cation oxidation state in the pyrazine system. Results of MNDO calculations for (1) and for 1,4-dihydro-benzene (4), -pyrazine (5), and -hexazine (6) indicate a contraction of bonds in the six-membered ring upon consecutive replacement of CH by N, accompanied by increasing deviation from planarity and decreasing π electron conjugation.