Conformation of a bicyclo[3,2,2]non-6-ene system: crystal and molecular structure of syn-3-exo-p-bromobenzoyloxybicyclo[3,2,2]non-6-ene-8,9-endo-cis-dicarboxylic acid anhydride

Abstract

The structure of syn-3-exo-p-bromobenzoyloxybicyclo[3,2,2]non-6-ene-8,9-endo-cis-dicarboxylic acid anhydride has been determined by a single-crystal X-ray analysis. The crystals are monoclinic, space group P2₁/c with Z= 4 in a unit cell of dimensions a= 13·47, b= 12·31, c= 10·63 Å, β= 117·5°. The structure was solved by the heavy-atom method and refined by least-squares calculations to R= 0·089 for 1977 reflections. This structure determination allows the identification of the epimeric products of the reaction of 1-benzoyloxyclohepta-3,5-diene and maleic anhydride. Twisting of the bicyclic skeleton about the axis through the bridgehead carbon atoms is not observed in the present instance, the relief of molecular strain being suggested by systematic valency-angle increases and by flattening of the three-carbon bridge.