Rotational isomerism of vinyl ethers of azines based on the data of IR spectroscopy and quantum-chemical AM1 calculations

The IR spectra of vinyl ethers of azines have two C=C stretching vibration bands of the vinyl group at 1620 and 1640 cm⁻¹, which correspond to thes-cis and nonplanars-trans conformers, respectively. According to the results of AM1 calculations, the hetaryl fragment and the vinyl group in thes-trans conformers of all the ethers under study are twisted out of the C−O−C plane by ∼30°. In thes-cis conformation, the angle of rotation of the heterocycle with respect to the vinyloxy group varies from 45 to 90°. The character of the change in the intensity of the v(C=C) absorption bands of the doublet under changes of the temperature indicates that thes-trans conformer is energetically favorable. The exception is 5-vinyloxyacridine for which thes-cis conformation is more favorable. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2439–2442, December, 1998.