Studies in the field of conformational snalyeis have led to the assignment of ccnfozmational free energy differences (-AFx) to a large number of substituents.' No information has appeared on the oonfonnatlcmal equilibrium of the trifluoromethyl group, whioh is of interest caupared vith other syuveetrical eubstituents (CH3, NH;, and i-Bu) bscsuse -OF,.,., 3 may be influenoed by attractive hydrogen-fluorine interaotiaas. An evaluation of the oonformational preference of the Mfluorcaethyl mp by infrared spectroscopy is now reported, ths method adopted being essentially that described by Pickering snd Prioe.* Judging from models it seemed likely that -AFcF would be at lort as great as -AF CH5 (and probably also -AFmT+) but5someshat lousr than -AF _+Bu ' SO that trifluorcmethyloyolohexene (I) should exit& predaeinsntly if not exclusively as oonfozmetion (Ie). This provsd to be the csse, end accordingly the mobile equilibrium of &-kmthyltrifluoomethylcyolohexane (11s +tIIe) wan studied in the e~eotation that the additional methyl group would alter conveniently the position of equilibria.