Microwave spectrum, molecular structure, barrier to internal rotation of methyl group, and ab initio MO calculation of 1-chloro-2-nitrosopropene, syn-ClCHC(CH 3)–NO

Abstract

syn-1-Chloro-2-nitrosopropene (ClCHC(CH 3)–NO) was generated by the vacuum solid–gas chemical reaction of 1,1-dichloro-2-(hydroxyimino)propane with anhydrous potassium carbonate. The product was identified by observing the microwave spectrum observed in the frequency range from 20 to 60 GHz. The rotational constants (MHz) for A symmetric species were determined to be A=8531(4), B=1470.00(2), and C=1263.56(2) for syn- 35ClCHC(CH 3)– 14NO ( 35Cl species), A=8517(10), B=1431.44(5), and C=1234.97(6) for syn- 37ClCHC(CH 3)– 14NO ( 37Cl species), and A=8451(8), B=1458.03(7), and C=1252.87(6) for syn- 35ClCHC(CH 3)– 15NO ( 15N species) in the ground vibrational states. The values of planar moment ( P cc =( I a + I b − I c )/2) obtained for 35Cl, 37Cl, and 15N isotopic species were 1.53(2), 1.58(5), and 1.52(5) uÅ 2, respectively. Those values suggest that the chlorine and nitrogen atoms lie in or are close to the a– b inertial axis plane of the molecule, and show that only two hydrogen atoms are located symmetrically out of the molecular symmetry plane. The reaction product was concluded to be syn-1-chloro-2-nitrosopropene by comparing the observed and calculated rotational constants, κ (Ray's asymmetry parameter), and r s coordinates of the chlorine and nitrogen atoms. Five structural parameters: r(C–CH 3), r(C–N), ∠Cl–CC, ∠CC–C, and ∠CC–N, were determined by least-squares fitting, using the six rotational constants ( B and C) of the three 35Cl, 37Cl, and 15N isotopic species. The barrier heights, V 3, to the internal rotation of the methyl group of 35Cl, 37Cl, and 15N isotopic species in the ground vibrational states were obtained to be 680(30), 680(30), and 687(30) cal/mol (1 cal/mol=4.184 J/mol).