Hindered Rotation I. The Configuration of the Cyclohexane Molecule

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Abstract
A restriction of the free rotation about the carbon‐carbon single bond will play an important role in the potential function of the cyclohexane molecule. Any force whose nature is such that it will produce a hindrance to the free rotation about the C–C bond must also give rise to different potential energies for the ``chair'' and ``tub'' forms of cyclohexane even if these forms are ``strainless'' in the Baeyer theory sense. According to the nature of the rotational restriction (stabilizing ``staggered'' or ``opposed'' configurations) either the ``chair,'' the ``tub,'' or even the hexagonally symmetrical form with a plane carbon ring could be the most stable form. From considerations of the obtained Raman spectra of cyclohexane, cyclohexane‐d1, and cyclohexane‐d12 it is shown that the only form present in measurable quantities is the form with a D6h symmetry, i.e., the form with the plane of the carbon ring as a reflection plane for the hydrogen atoms. The rotational restriction about the C–C single bond, therefore, is of such a nature that it stabilizes this D6h configuration, in which the H atoms are in ``opposed'' positions.