Rotational spectrum of vinyl fluoride center dot center dot center dot ClF: Are the pi-bonding or nonbonding electrons the most nucleophilic region of vinyl fluoride?

The ground-state rotational spectra of C2H3F ...(ClF)-Cl-35 and C2H3F ...(C lF)-Cl-37 have been observed with a pulsed-nozzle, Fourier-transform microw ave spectrometer. Rotational constants (A(0), B-0, C-0), centrifugal distor tion constants (Delta(J), Delta(JK), delta(J), delta(K)) and the Cl nuclear quadrupole coupling tensor chi(alpha beta) (alpha, beta = a, b, c) Were de termined in each case. A detailed interpretation of the chi(alpha beta) ten sor leads to the conclusion that the complex is nearly planar and that the interaction between the vinyl fluoride and CIF subunits is weak. The direct ion cosines Phi(alpha z) (alpha = a, b or c) associated with the CIF z axis and the principal inertial axes were determined together with the principa l components chi(zz), chi(xx), chi(gamma gamma) Of the Cl nuclear quadrupol e coupling tensor. The geometry of the complex was obtained by fitting the rotational constants of the two isotopomers under the constraint that the r esulting geometry must reproduce the Phi(alpha z). The CIF molecule was fou nd to form a nearly linear 'chlorine' bond F ... Cl-F (deviation from colli nearity theta = 0.6 degrees) to the F atom of vinyl fluoride, with r(F ... Cl) = 2.719(5) Angstrom and the angle C(1)F ... Cl = 125.7(3)degrees. A com parison with the geometry of vinyl fluoride ... HCl, determined in the same way, revealed the angular geometries of the Cl and HCl complexes of vinyl fluoride to be isomorphous, except for a significant deviation (theta = 18. 3 degrees) of the hydrogen bond in C2H3F ... HCl from collinearity.