The vibrational spectra and conformations of 2,2-di (fluoromethyl)-1,3- difluoropropane

Abstract

The IR spectra of the title compound were recorded as a vapour, liquid, as a solute in solvents of different polarity, as a plastic and crystalline solid at low temperatures and at high pressure, as well as in matrix isolation spectra in argon and nitrogen matrices, using the hot nozzle technique. Raman spectra of the liquid, of solutions and of the plastic phase were recorded at different temperatures, and spectra of the crystalline solid was obtained. Among the six possible staggered conformers: D 2d, S 4, C 1, C 1 *, C 2 and C s all but the last two have been detected in the spectra. The two most stable conformers are S 4 and D 2d without 1,3 parallel C-F interactions, of which S 4 is ca. 1 kJ mol −1 lower in energy than D 2d, and is present in the low temperature and in the high pressure crystals. The C 1 and C 1 * conformers have dipole moments around 2 D, and the bands are strongly enhanced at 700 K as well as in polar solvents. The enthalpy differences ΔH 0 have been calculated from variable temperature measurements in the plastic phase and in the matrices, and confirmed by Gaussian 90 with basis set 6–31G * and 6–31G and by semiempirical and molecular mechanics calculations: MNDO, AM1 and MM2.