Generation, Microwave Spectrum, Barrier to Internal Rotation of Methyl Group, and ab Initio MO Calculation of syn-2-Nitrosopropene, syn-CH(2)&dbond;C(CH(3))&bond;N&dbond;O.

ABSTRACT

syn-2-Nitrosopropene was generated, in the gas phase, by chemical reaction of 1-chloro-2-(hydroxyimino)propane with K(2)CO(3) and identified by microwave spectroscopy. The microwave spectrum of the reaction product was observed in the frequency range from 8.0 to 40.0 GHz. The rotational constants (MHz) were determined as A = 8744.09(6), B = 4846.07(2), and C = 3177.84(3) for CH(2)&dbond;C(CH(3))&bond;(14)NO (normal species) and A = 8664.36(5), B = 4822.15(3), and C = 3157.04(3) for CH(2)&dbond;C(CH(3))&bond;(15)NO ((15)N species) in the ground vibrational state. The values of the planar moment (P(cc) = (I(a) + I(b) - I(c))/2) obtained for the normal and (15)N species were 1.525(1) and 1.526(1) u Å(2), respectively. This suggests that the nitrogen atom lies in or is close to the ab inertial plane of the molecule and shows also that only two hydrogen atoms are located symmetrically out of the symmetry plane. The reaction product was determined to be syn-2-nitrosopropene by comparing the observed and calculated rotational constants, kappa (Ray's asymmetry parameter) and r(s) coordinates of the nitrogen atom. The dipole moments (D) were determined to be µ(a) = 2.43(5), µ(b) = 1.12(7), and µ(total) = 2.67(7). The barrier heights of the internal rotation owing to the methyl group of the normal species in the ground and first excited torsional states were determined to be 1750(50) and 1740(50) cal/mol (1 cal/mol = 4.184 J/mol), respectively. The (14)N nuclear quadrupole coupling constants (MHz) were determined to be chi(aa) = 0.25(21), chi(bb) = -7.11(40), and chi(cc) = 6.85(61). Two vibrational excited states were observed and the vibrational frequencies (cm(-1)) of the C-N and C-C torsional modes were determined to be 160(40) and 175(40), respectively. The lifetime of syn-2-nitrosopropene was found to be ca. 2 min in the waveguide cell. Copyright 2000 Academic Press.