Molecular structure of dichloroacetaldehyde oxime by gas-phase electron diffraction combined with microwave spectroscopy

The gas-phase structure of dichloroacetaldehyde oxime (Cl2CH-CH=NOH, DCAO), was determined by gas-phase electron diffraction (GED) combined with micro wave (MW) spectroscopic data. The nozzle temperature in the GED experiment was about 53 degrees C. Structural constraints in the GED data analysis wer e obtained by the ab initio MO calculation of DCAO at the MP2/6-31G(d, p) l evel of theory. Vibrational amplitudes, shrinkage corrections for the data analysis of GED and vibrational corrections of the experimental rotational constants were calculated from the harmonic force constants given by normal coordinate analysis. The (E)-isomer with the dihedral angle of phi(ClCCN) = 119.7(2)degrees was the dominant conformer. The MW spectroscopic investig ation and the optimized structure in the ab initio calculations were consis tent with the present result. The population of the dominant conformer was 80(1)%. The results of the data analysis indicated that there were two othe r conformers involved, whose conformations and populations were: (E)-isomer with one chlorine atom on the plane of the molecular skeleton (10(1)%) and (Z)-isomer with phi of about 105 degrees (10(1)%). The principal bond dist ances and angles (r(g)/Angstrom and angle(alpha)/deg) of the dominant confo rmer, (E)-isomer, were: r(C-C) = 1.497(8); r(C=N) = 1.281(4); r(C-Cl) = 1.7 84(2); r(N-O) = 1.415(4); angle CCN = 117.0(8); angle CCCl = 109.4(3); angl e CNO = 111.1(5); and angle NOH = 97.2(50). The values in parentheses were three times the standard deviations. (C) 1999 Elsevier Science B.V. All rig hts reserved.