X-ray crystallographic and molecular orbital studies on the conformation of tryptamine

The crystal structure of neutral tryptamine has been determined by X-ray methods. The refinements result in a conventional R value of 0.043. Tryptamine molecules are held together to form layered structures perpendicular to the c axis by van der Waals contacts and by N-H...N type hydrogen bonds. The conformation is similar to that of other cationic tryptamines. By the conformational energy calculation which was carried out by the Complete Neglect of Differential Overlap (CNDO/2) method, it is shown that the folded conformation observed in this crystal structure is attributed mainly to the nature of tryptamine molecule. Furthermore, it seems likely that this conformation is also significant and common in other numerous unsubstituted indolealkylamines, because their conformations are similar to that of the tryptamine.