QUANTUM-CHEMICAL STUDY OF ELECTRONIC-PROPERTIES OF MODEL SPIROOXAZINES

Model spirooxazines were studied via ab initio quantum-chemical calcul ations. An anomeric interaction between nitrogen lone pair and antibon ding orbital of the C-spiro-O bond has been considered by Hartree-Fock SCF level of theory with 3-21G basis set. The extent of the n(N)-sigm a(CO) interaction has been shown to depend on planarity of the nitroge n atom, being maximized with its planarity growth. Electronic properti es and geometry parameters of model spirooxazines were considered by l imited CI under 3-21G basis set. Excitation lengthens the C-spiro-O bo nd and causes a significant polarization of total wave function, which results in increasing of the system dipole moment and transferring th e electronic density from the O2 atom and the phenyl fragment onto the N13=C14 bond in the case of spirooxazine and onto the NO2 group in th e case of nitro-spirooxazine. Elongation of the C-O bond under excitat ion is due to the NO2 interaction in spirooxazines. CI calculation of the excited singlet state of a model chromene does not show elongation of this bond. (C) 1997 Elsevier Science B.V.