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

The gas-phase structure of dichloroacetaldehyde oxime (Cl 2 CH–CH NOH, DCAO), was determined by gas-phase electron diffraction (GED) combined with microwave (MW) spectroscopic data. The nozzle temperature in the GED experiment was about 53°C. Structural constraints in the GED data analysis were obtained by the ab initio MO calculation of DCAO at the MP2/6-31G(d, p) level 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 φ (ClCCN)=119.7(2)° was the dominant conformer. The MW spectroscopic investigation and the optimized structure in the ab initio calculations were consistent with the present result. The population of the dominant conformer was 80(1)%. The results of the data analysis indicated that there were two other 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 φ of about 105° (10(1)%). The principal bond distances and angles ( r g /A and ∠ α /deg) of the dominant conformer, ( E )-isomer, were: r (C–C)=1.497(8); r (C N)=1.281(4); r (C–Cl)=1.784(2); r (N–O)=1.415(4); ∠CCN=117.0(8); ∠CCCl=109.4(3); ∠CNO=111.1(5); and ∠NOH=97.2(50). The values in parentheses were three times the standard deviations.