Microwave Spectrum, Structure, Dipole Moment, and Nuclear Quadrupole Effects in Vinyl Chloride

Abstract

The microwave spectra of nine isotopic species of vinyl chloride have been measured and analyzed, yielding moments of inertia from which a molecular structure was calculated. The bond lengths found are (in A) C=C 1.33₂, C–Cl 1.72₆, average C–H 1.08. The bond angles are C₂C₁Cl 122°, C₂C₁H₁ 124°, C₁C₂H₃ (cis to Cl) 121°, C₁C₂H₂ (trans to Cl) 120°. Planarity was assumed. The chlorine nuclear quadrupole hyperfine lines were reexamined. From the data for several isotopic species it was shown that the C–Cl bond direction is within five degrees of a principal axis of the field gradient tensor. The lack of cylindrical symmetry of the field gradient about the C–Cl bond was confirmed. This is evidence that the observed shortening of the C–Cl bond is at least in part due to conjugation with the C=C double bond and not solely to hybridization effects. The component of dipole moment along the a inertial axis was found to be 1.42±0.02 D.