Rotational spectroscopy and molecular structure of the 1,1,2-trifluoroethylene-hydrogen chloride complex.

Fourier transform microwave spectra in the 6-20 GHz region are obtained for the complex formed between 1,1,2-trifluoroethylene and hydrogen chloride, including both (35)Cl and (37)Cl isotopomers. Analysis of the spectra provides rotational constants and additionally, the complete quadrupole hyperfine coupling tensor in both the inertial and principal electric field gradient axis systems. The inertial information contained in the rotational constants combined with the results of the hyperfine analysis provides the structure for CF(2)CHF-HCl. A primary, hydrogen bonding interaction exists between the HCl donor and the F atom geminal to the H atom on the substituted ethylene. The hydrogen bond is bent from linearity to allow a secondary interaction to form between this H atom and the Cl atom. Comparisons made to similar complexes involving both other protic acids (HF and HCCH) and fluoroethylenes (vinyl fluoride and 1,1-difluoroethylene) reveal the effects of varying gas phase hydrogen bond donor strength, of increasing fluorine substitution on fluorine atom nucleophilicity, and on the relative importance of steric versus electrostatic effects in determining the structures of these species.