Study of conformational changes in trisalicylides by nuclear magnetic resonance spectroscopy

Abstract

The cyclic trianhydro-derivatives, tri-o-carvacrotide, tri-o-thymotide, and tri-3,6-dimethylsalicylide have been shown by n.m.r. spectroscopy to exist in chiral non-planar conformations of propeller and helical types. The rates of interconversion of these conformations are such that they may be studied by examination of the line-shapes of temperature-dependent n.m.r. signals. The activation parameters for conformational interconversion have been obtained, and for the case of tri-o-thymotide the results may be compared with those previously obtained from a polarimetric study of the racemisation of optically active tri-o-thymotide. The conformation of tri-o-thymotide in crystalline clathrate compounds has been shown to be of the propeller type.