Rotational spectra of two isotopomers of the 2,5-dihydrofuran/CIF complex were observed by using the fast-mixing nozzle/Balle-Flygare spectrometer combination. The complex has C s symmetry and a pyramidal configuration at oxygen. The angle between the 3 5 ClF axis (z) and the a-axis, α a z = 17.95(3)°, was determined from the Cl nuclear quadrupole coupling tensor. The geometry r(O Cl) = 2.422(5) 9, φ = 127.0(3)° and θ = 1.99(15)° is established when rotational constants are fitted under the constraints of unpertubed monomers and α a z = 17.95(3)°. The configurations φ at O and the nonlinearities θ of the B ClF/B HCl systems are compared for B = 2,5-dihydrofuran and oxirane.