ChemInform Abstract: ELECTRON‐DIFFRACTION STUDY OF THE STRUCTURE OF 1,2,7,8‐DIEPOXYOCTANE

Abstract

The molecular structure of gas‐phase 1,2,7,8‐diepoxyoctane was investigated by electron diffraction to extend a study of straight‐chain diepoxides. The synthesis of diepoxyoctane results in a mixture of two diastereomers, which considerably complicates the conformational problem. The distribution of trans and gauche conformers arising from the rotation around the three central C–C bonds was calculated by assuming a free‐energy difference of 610 cal/mole between the trans and gauche positions. The positions of major nonbonded peaks in the radial distribution then ruled out all but two orientations (A and B) of the epoxy groups. The end‐carbon atoms in conformation A are displaced from the trans position (by about 40°) and the oxygen atom is in a roughly gauche position. In conformation B the positions of the end‐carbon atom and the oxygen atom are approximately interchanged with respect to their positions in conformation A. With the assumption that only one orientation was allowed, the angles defining orientations A and B were optimized and a significantly lower standard deviation was obtained with the former. However, without reoptimizing any of the angles, it was found that models involving combinations of orientations A and B gave as good agreement as the model with A alone. The best of the mixed models coupled the orientation of the end group with the conformation of the central carbon atoms. Since consideration of mixed models essentially doubles the number of parameters to be determined, the present experiment was not able to establish completely the distribution of conformers.