Microwave Spectrum and Molecular Structure of (Z)-Chloroacetaldehyde Oxime

Abstract

The microwave spectra of (Z)-35ClCH2CH=NOH, (Z)-37ClCH2CH=NOH, (Z)-35ClCH2CH=NOD, and (Z)-37ClCH2CH=NOD have been observed in the frequency range from 16.5 to 40.0 GHz. The rotational and centrifugal distortion constants of four isotopic species and the nuclear quadrupole coupling constants of the35Cl species were determined. The values of planar moment (Pcc= (Ia+ Ib− Ic)/2) obtained for four isotopic species were found to be 1.761(14), 1.800(18), 1.777(19), and 1.770(18) u Å2in the ground vibrational state. The unchanged values ofPccshow that the chlorine and hydroxyl hydrogen atoms lie in or are very close to theabinertial plane of the molecule. The conformation of theZ-form was determined to be Calcd I (φ1= 180°, φ2= 180°), as shown in Fig. 1, from the comparison of the observed and calculated rotational constants and coordinates of the chlorine and hydroxyl hydrogen atoms. The determined conformation is consistent with that reported by an electron diffraction study (K. Iijima, T. Hanamori, T. Sakaizumi, and O. Ohashi,J. Mol. Struct.299,149–153 (1993).). One excited vibrational state is assigned to the C–C torsional mode, and it is anharmonic. This fact is also consistent with the result of a large amplitude motion about the C–C single bond reported by a gas-phase electron diffraction study. Assuming the skeleton of the heavy atoms is a planar molecule, the seven structural parameters of theZ-form (anti-form) were fitted to the eight rotational constants (BandC) of four isotopic species. The obtained structural parameters (r0) are almost the same as those obtained by electron diffraction study (rα) within the errors.