Fluorine NMR Spectra and Conformational Isomerization of 1,1-Difluorocyclohexane

The 19F high-resolution spectrum of 1,1-difluorocyclohexane has been observed at temperatures from −93° to +40°C. The rate of conformational isomerization was determined by a complete line-shape analysis method for temperatures from −71° to +6°C. Activation parameters ΔH‡ and ΔGcc‡ in kilocalories/mole and ΔScc‡ in entropy units were 9.0, 9.8, −3.3 and 8.6, 9.8, −5.0 for 1:1 vol/vol solutions in CS2 and CFCl3, respectively, at the coalescence temperature of 228°K. In the low-temperature spectra of the CS2 solution, the resonance of the equatorial fluorine is shifted 15.64 ppm downfield from the axial and JFF is 235.3 cps; also J (Hax–Fax) the axial-axial vicinal H–F coupling constant is 34.3 cps and J (Heq–Fax) is 11.5 cps. At temperatures above −10°C, neglect of the H–F coupling in the line-shape analysis produces systematic errors in the apparent exchange rate.