AM1 studies of photoelectron spectra - 12. Photoelectron spectrum and stereoisomerism of 10-vinylphenothiazine

Empirical analysis of the photoelectron spectrum of 10-vinylphenothiazine demonstrated that in the gaseous phase, this compound exists as two stereoisomers that differ in the electronic structure. One of them contains the planar amine fragment. The second stereoisomer is characterized by the quasi-axial orientation of the substituent. The X-ray diffraction data for the molecules and donor-acceptor complexes of phenothiazine derivatives as well as for the radical-cation of 10-ethylphenothiazine were used for obtaining structure correlations. These correlations and the results of AM1 calculations indicate that pyramidal inversion of the nitrogen atom occurs simultaneously with inversion of the ring. In the stereoisomer containing the planar heterocyclic fragment, the dihedral angle between the planes of the benzene rings is 180 degrees. According to the data of photoelectron spectroscopy, this stereoisomer is characterized by a substantial deviation of the vinyl group from the plane of the heteronucleus. In the stereoisomer with the quasi-axial arrangement of the substituent, the dihedral angle between the planes of the benzene rings is 150 degrees. Similar values of the angles were obtained in the AM1 calculations of the potential of internal motion of 10-vinylphenothiazine.