THE VIBRATIONAL-SPECTRA AND CONFORMATIONS OF POLYHALOGENATED CYCLOBUTANES

The vibrational spectra of 1-chloro-2,2,3,3-tetrafluoro- and 1-cyano-2,2,3,3-tetrafluorocyclobutane reveal that these compounds have a conformational equilibrium strongly shifted towards equatorial Cl and CN substituents, although to a smaller extent than for the chloro and cyanocyclobutane. When a Cl and an F atom are attached to the same carbon, they will compete for the preferred equatorial position, giving relatively small enthalpy differences between the conformers. In 1-chloro-1-fluoro-, 1-chloro-1,2,2-trifluoro- and 1,1,2-trichloro-2-3,3-trifluorocyclobutane the enthalpy differences are 2.2, 2.9 and 0.9 kJ mol-1 in the liquid, respectively. In 1-chloro-1,2,2-trifluro and 1,1,2-trichloro-2,3,3-trifluorocyclobutane the ring puckering barrier was ca. 6-7 kJ mol-1, for the remaining compounds it was smaller than 5 kJ mol-1. © 1990.