Generation, microwave spectrum, and ab initio MO calculation of trans-1-nitrosopropene, CH3CH = CH-NO (syn form)

trans-1-Nitrosopropene (syn form) was generated in the gas phase by pyrolys is of 1-chloro-1-methyl-2-(hydroxyimino)ethane and identified by microwave spectroscopy. The microwave spectrum of the pyrolysate was observed in the frequency range from 8.0 to 40.0 GHz. The rotational constants (MHz) were d etermined as A = 34 025(390), B = 2315.62(2), and C = 2198.54(2) for CH3CH= CH-NO (normal species) and A = 34 012(530), B = 2300.04(3), and C = 2182.70 (2) for CH3CH=CH-(NO)-N-15 (N-15 isotopic species) in the ground vibrationa l state. The values of planar moment (P-cc = (I-a + I-b - I-c)/2) obtained for the normal and N-15 isotopic species were found to be 1.62(10) and 1.52 (13) u Angstrom(2), respectively. These values are almost the same within t he limit of errors. This suggests that the nitrogen atom lies in or is clos e to the nb inertial plane of the molecule and shows also that only two hyd rogen atoms are located symmetrically out of the symmetry plane. The pyroly sate was determined to be trans-1-nitrosopropene by comparing the observed and calculated rotational constants, kappa (Ray's asymmetric parameter), an d r(s) coordinates of the nitrogen atom. One vibrationally excited state wa s observed and assigned to the C-N torsional mode (158(50) cm(-1)). Interes ting pyrolysates such as hydrogen cyanide and acetaldehyde were also detect ed during the pyrolysis of the precursor. The lifetime of trans-1-nitrosopr opene is found to be ca. 5 s in the waveguide cell. (C) 1999 Academic Press .