Conformations of tetrahydro-2-(non-1-en-3,5,7-triynyl)pyran-3-acetate (cunaniol acetate). Part 1. Crystal and molecular structure of cunaniol acetate (violet modification)

Abstract

The three-dimensional structure of the title compound, a naturally occurring polyacetylene which is a potent convulsant drug, has been determined by single-crystal X-ray diffraction methods. Crystals are orthorhombic, space group P2₁2₁2₁ with a= 17.512(12), b= 16.378(10), c= 5.128(3)Å, Z= 4. The structure was solved by direct methods and refined by a least-squares procedure to R 0.049 for 538 observed diffraction maxima. The tetrahydropyran ring is in an undistorted chair conformation with the polyacetylene chain and acetate groups equatorial. The violet colour of the crystals is discussed in terms of the molecular packing which is determined by van der Waals forces.