W0053

Conformations of C-Substituted Triazacyclohexanes. William H. Ojala, Courtney E. Irwin, Jeffrey E. Caudill, and J. Thomas Ippoliti, Dept. of Chemistry, Univ. of St. Thomas, St. Paul, MN 55105.

Several examples of 1,3,5-triazacyclohexanes bearing aryl substituents on the nitrogen atoms of the heterocyclic ring have appeared in the crystallographic literature, and their conformations, particularly the orientations of the aryl groups, have been described in detail. In contrast, few structures of triazacyclohexanes substituted at the carbon atoms of the heterocyclic ring have been published, and none of these heterocycles bear aryl groups. We describe here the crystal and molecular structures of the C-substituted 1,3,5-triazacyclohexanes I-IV. These compounds are readily prepared by bubbling anhydrous ammonia through an acetonitrile solution of the aldehyde of choice; crystals suitable for X-ray analysis appear on standing. The aryl rings of N-substituted triazacyclohexanes have been found to assume equatorial-diaxial orientations in the solid state that minimize interactions between lone pairs of electrons, but in the C-substituted compounds I-IV the solid-state orientation of the aryl rings is triequatorial in each case. The heterocyclic ring assumes a chair conformation in which the orientations of the N-H bonds are axial, placing the lone pairs of electrons in equatorial positions in all four structures. In I-III the aryl rings are nearly coplanar with the mean plane through the central heterocyclic ring, giving the molecules a flattened shape. In contrast, the pyridyl rings of IV are more nearly perpendicular to the plane of the central heterocycle.