Quantum chemical description of the molecular vibration spectra. treatment of the three-membered N-Heterocycles

The Vibration frequencies and IR adsorption intensities were calculated for cyclopropene, 1a-azirine, 2Hazirine and aziridine, applying the MINDO/3-Forces and ab into methods, and assigned to their corresponding symmetry representations and valance modes, for cyclopropene a C=C stretch, V3, rather than a ring results, of wi berg et al, for 1a-airing, it is found that symmetric C-H frequency os higher than the antisymmetric, The Nh stretch vibration is completely localized at the H n atom (App.) =0.95). This hand shows the highest absorption frequency in the spectrum. For 2a-azirine, the =C-H stretch vibration is localized at the H atom,. Further, the frequency of the symmetric CH2 (a) stretch is approximately equal to that the CH2 (a') stretch is approximately equal to that of the CH2 antisymmetric. As for aziridine, the V1 (a') Nh stretch shows the shows the highest absorption intensity value. It sl so shows a significant contribution of motion from the CH' atoms, V2 (a') and V3 (a') are Ch stretch and not CH2 stretch vin rations. Due to the close values of frequencies it is predicted that V3 (a) for Ch and V11 (a') for CH2 should overlap when measured experimentally. (authors). 24 refs., figs., 7 tabs