CYCLOHEXYL RINGS IN SPATIAL PROXIMITY - STEREOCHEMISTRY OF TRICYCLOHEXYLMETHANE

The static and dynamic stereochemistry of tricyclohexylmethane (2) is analyzed. The C-13 and H-1 NMR of 2 were assigned by means of the 2D N MR techniques INADEQUATE and DQF COSY. Molecular mechanics calculation s were performed in order to estimate the influence of the torsional a ngles of the cyclohexyl rings and their mode of attachment (equatorial or axial) on the relative energy of the conformations. MM3 calculatio ns of 2 indicate that in the lowest energy conformation the cyclohexyl rings are attached to the central carbon via their equatorial positio ns and are oriented in a chiral gauche,gauche,anti (g,g,a) arrangement . The compound crystallizes in two crystalline forma. X-ray diffractio n 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 enantio mers are present. Upon lowering the temperature, decoalescence was obs erved in the C-13 NMR signals, and a barrier of 7.3 +/- 0.2 kcal mol-1 was calculated for the rotational process. The conformational interco nversion of 2 was calculated by MM3 calculations which indicate that t he process followed by NMR corresponds to an enantiomerization process .