Carbon—hydrogen stretching vibrations in fluorocyclohexanes

For perfluorocyclohexane derivatives in which not more than one fluorine at each carbon atom is replaced by a hydrogen atom, it is established that C---H groups with an axial hydrogen show infra-red absorption at 2980 cm⁻¹ and with equatorial hydrogen at 2974 cm⁻¹. With 1H/2H-, 1H:2H/- and 1H:3H/-decafluorocyclohexane the frequencies are reduced somewhat. When the C---H groups are adjacent to a double bond the absorption is at 2961 cm⁻¹, while olefinic C---H groups absorb near 3095 cm⁻¹ in the fluorocarbon series. The C---H absorption is at 3102 cm⁻¹ in pentafluorobenzene.