Cyclohexyl Rings in Spatial Proximity: Stereochemistry of Tricyclohexylmethane

The static and dynamic stereochemistry of tricyclohexylmethane (2) is analyzed. The ¹³C and ¹H NMR of 2 were assigned by means of the 2D NMR techniques INADEQUATE and DQF COSY. Molecular mechanics calculations were performed in order to estimate the influence of the torsional angles of the cyclohexyl rings and their mode of attachment (equatorial or axial) on the relative energy of the conformations. MM3 calculations of 2 indicate that in the lowest energy conformation the cyclohexyl rings are attached to the central carbon via their equatorial positions and are oriented in a chiral gauche,gauche,anti (g,g,a) arrangement. The compound crystallizes in two crystalline forms. X-ray diffraction analysis of 2 indicates that, in both crystals, the conformation is (g,g,a), but in the higher melting form only homochiral molecules are packed in a single crystal while in the lower melting one both enantiomers are present. Upon lowering the temperature, decoalescence was observed in the ¹³C NMR signals, and a barrier of 7.3 ± 0.2 kcal mol⁻¹ was calculated for the rotational process. The conformational interconversion of 2 was calculated by MM3 calculations which indicate that the process followed by NMR corresponds to an enantiomerization process.