15min:
THE STRUCTURE OF THE 1-CHLORO-1-FLUOROETHYLENE--ACETYLENE COMPLEX.

HELEN O. LEUNG, MARK D. MARSHALL AND DAVID D. GRIMES, Department of Chemistry, Amherst College, P.O. Box 5000, Amherst, MA 01002-5000.

The insensitivity of the moments of inertia to certain geometric parameters for the limited set of isotopologues studied led to unexpected results for a preliminary structure of the complex formed between 1-chloro-1-fluoroethylene and acetylene presented three years ago. The availability of this chlorofluoroethylene with a single deuterium substitution in both ( E ) and ( Z ) isomeric forms allows us to supplement the original data set with microwave spectra of ( E )-CHDC35ClF--HCCH and ( Z )-CHDC35ClF--HCCH. Supported by the results of ab initio calculations, a planar, chemically reasonable structure is obtained for this complex, in which the acetylene forms a hydrogen bond with the fluorine atom of 1-chloro-1-fluoroethylene. The hydrogen bond bends to allow a secondary interaction with the hydrogen atom cis to this fluorine atom. Comparisons with the structure of the analogous complexes formed with vinyl fluoride and 1,1-difluoroethylene reveal the effects of chlorine substitution geminal to the acceptor atom of the hydrogen bond.