VIBRATIONAL-SPECTRA AND CONFORMATIONS OF 1-CHLORO-2,2,3,3-TETRAFLUOROCYCLOBUTANE AND 1-CYANO-2,2,3,3-TETRAFLUOROCYCLOBUTANE

The IR and Raman spectra of 1-chloro- and 1-cyano-2,2,3,3-tetrafluoroc yclobutane were recorded in various phases and at different temperatur es, including IR matrix spectra in argon and in nitrogen matrices usin g the hot nozzle method.Both compounds had two conformers in the vapou r and liquid states, while they crystallized as one distinct conformer . All the bands vanishing in the crystal spectra had low intensities i n the vapour and liquid states. The matrix spectra of both compounds c ontained only one conformer at 13 K as well as at 4.8 K, revealing tha t the high-energy conformers were not trapped. Thus, a barrier below 2 .0 kJ mol-1 from the axial to the equatorial (Cl or CN substituents) c onformers is suggested for both molecules. The enthalpy difference DEL TAH-degrees between the conformers in the liquid was 3.4 +/- 0.7 kJ mo l-1 for the chloro compound and 3.9 +/- 0.9 kJ mol-1 for the cyano com pound. From ab initio calculations with the 3-21G and 6-31G* basis se ts, the enthalpy differences 4.2 and 6.2 kJ mol-1, respectively, were obtained for the chloro compound. Fairly complete assignments of the e -conformer spectra were made for both molecules with the aid of force- constant calculations derived from scaled ab initio force constants fo r the chloro, and on transferred force constants for the cyano compoun d.