Crystal and molecular structure of cis-6-chloro-trans-7-chloro-cis-bicyclo[3,2,0]heptan-2-one

Abstract

The major product of photocycloaddition of cis-dichloroethylene to 2-cyclopentenone is established by a single-crystal X-ray diffraction study to be cis-6-chloro-trans-7-chloro-cis-bicyclo[3,2,0]heptan-2-one. The configuration found is consistent with the suggestions that photoaddition begins at C(3) of the ketone and that rotational equilibration of the diradical intermediates is completed before ring closure.

This isomer of C₇H₈Cl₂O crystallizes in space group P2₁/c, with Z= 4 in a unit cell of dimensions a= 6·191, b= 11·172, c= 11·709 (Å), and β= 94·73°. The structure was solved from diffractometer data by reiterative application of Sayre's equation and refined by full-matrix least-squares to R 0·056 for the 1236 reflections above background. Both the four- and five-membered rings are markedly nonplanar.