The Microwave Spectrum and Molecular Structure of (E)-1-Chloro-2-Fluoroethylene-HF: Revealing the Balance among Electrostatics, Sterics, and Resonance in Intermolecular Interactions.

Abstract

The structure of the gas-phase bimolecular complex formed between (E)-1-chloro-2-fluoroethylene and hydrogen fluoride is determined via Fourier transform microwave spectroscopy from 6.9-21.6 GHz. Although the complex adopts a geometry very similar to that of previously studied dihalosubstituted ethylene-HF species, trends observed in the values of structural parameters such as bond lengths, bond angles, and deviations of the primary hydrogen-bonding interaction from linearity provide information regarding the balance among electrostatic, steric, and resonance effects in the structures of these complexes. Consideration of the ab initio interaction potential between (E)-1-chloro-2-fluoroethylene and hydrogen fluoride suggests that it is the strength of the intermolecular bond formed between the hydrogen atom of HF and the fluorine atom of the substituted ethylene that plays the significant role in determining the geometry. In addition to determining the complete nuclear quadrupole coupling constant tensor for the (E)-1-chloro-2-fluoroethylene-HF complex, the corresponding tensor for (E)-1-chloro-2-fluoroethylene itself was measured with greater precision than previously availabe, including the first reported determination of the single, nonzero off-diagonal element, χab.