Quantum-chemical study of electronic properties of model spirooxazines

Model spirooxazines were studied via ab initio quantum-chemical calculations. An anomeric interaction between nitrogen lone pair and antibonding 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-σ*_CO interaction has been shown to depend on planarity of the nitrogen atom, being maximized with its planarity growth. Electronic properties and geometry parameters of model spirooxazines were considered by limited CI under 3-21G basis set. Excitation lengthens the C_spiro-O bond and causes a significant polarization of total wave function, which results in increasing of the system dipole moment and transferring the 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 the case of nitro-spirooxazine. Elongation of the C-O bond under excitation 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.