Crystal and molecular structures of norbornene

Abstract

Abstract The ordered, low-temperature phase of the globular organic molecule norbornene, (bicyclo[2.2.1]hept-2-ene, C7H10), has been determined by high resolution powder X-ray diffraction using synchrotron radiation, by auto-indexing, then by intensity extraction and direct methods using the EXPO package. The structure is monoclinic, space group P21/c, Z = 4, with a = 7.6063(9) Å, b = 8.6220(1) Å, c = 8.749(1) Å, β = 97.24(1)° at 85 K. The structure was refined whilst restraining the molecule to m (Cs) symmetry as found in the gas phase. The molecular structure agrees with that obtained from ab-initio molecular orbital calculations, and is less distorted than that obtained from a previous solution of the structure involving an unrestrained refinement from conventional powder X-ray diffraction data (Min, Benet-Buchholz and Boese, 1998). Norbornene starts to transform to the hexagonal close-packed, orientationally-disordered, room-temperature form at around 116 K on warming.