Rotational spectrum of vinyl fluoride···ClF: Are the π-bonding or nonbonding electrons the most nucleophilic region of vinyl fluoride?

Abstract

The ground-state rotational spectra of C₂H₃F···³⁵ClF and C₂H₃F···³⁷ClF have been observed with a pulsed-nozzle, Fourier-transform microwave spectrometer. Rotational constants (A₀, B₀, C₀), centrifugal distortion constants (Δ_J, Δ_JK, δ_J, δ_K) and the Cl nuclear quadrupole coupling tensor χ_αβ (α, β=a, b, c) were determined in each case. A detailed interpretation of the χ_αβ tensor leads to the conclusion that the complex is nearly planar and that the interaction between the vinyl fluoride and ClF subunits is weak. The direction cosines Φ_αz (α=a, b or c) associated with the ClF z axis and the principal inertial axes were determined together with the principal components χ_zz, χ_xx, χ_yy of the Cl nuclear quadrupole coupling tensor. The geometry of the complex was obtained by fitting the rotational constants of the two isotopomers under the constraint that the resulting geometry must reproduce the Φ_αz. The ClF molecule was found to form a nearly linear ‘chlorine’ bond F···Cl–F (deviation from collinearity ϑ=0.6°) to the F atom of vinyl fluoride, with r(F···Cl)=2.719(5) Å and the angle C(1)F···Cl=125.7(3)°. A comparison with the geometry of vinyl fluoride···HCl, determined in the same way, revealed the angular geometries of the ClF and HCl complexes of vinyl fluoride to be isomorphous, except for a significant deviation (ϑ=18.3°) of the hydrogen bond in C₂H₃F···HCl from collinearity.