Principal Field-Gradient Tensor in 1,1-Difluoro-2-Chloroethylene and Bonding in the Substituted Ethylenes

Abstract

The microwave spectrum of F2C=CH35Cl has been re-examined to determine the off-diagonal element of the nuclear quadrupole coupling tensor. The rotational constants are A = 10 710.72 ± 0.02 MHz, B = 2297.12 ± 0.01 MHz, and C = 1890.17 ± 0.01 MHz. The nuclear quadrupole coupling constants in the principal inertial axis system are χaa = −55.05 ± 0.10 MHz, χbb = +18.29 ± 0.08 MHz, and χcc = +36.76 ± 0.10 MHz. Second-order quadrupole coupling effects have been used to measure the nonzero off-diagonal element in the χ tensor (in the molecular plane) as χab = ±46.3 ± 4 MHz. The in-plane C–Cl bond-axis coupling constants are also given as χαα = −77.40 MHz and χββ = +40.64 MHz which agree well with similar molecules. The quadrupole coupling constants in several substituted chlorethylene molecules are interpreted in terms of effects on the carbon–chlorine bond.