Topochemistry. Part XXIX. Crystal and molecular structures of p-methoxychalcone

Abstract

The crystal structure of 4-methoxychalcone (4-methoxybenzylideneacetophenone) has been solved from photographically recorded partial three-dimensional data and refined to R′ 0·022 and R 0·063. The C–C and C–O bond lengths have been determined with estimated standard deviations of 0·010 Å; the molecule consists of the three planar units MeOC₆H₄, CHCH–CO, and C₆H₅, the angle between the planar units being 4·5 and 11·5°.

The molecules are packed in two sets of screw-axis related stacks along the a axis; the shortest contact (4·2 Å) of CC groups occurs in the stacks along [100]; all other contacts are >5 Å. The formation of the cyclobutane dimer of molecular symmetry m therefore follows the topochemical rules deduced in the photo-cyclo-dimerisation of αβ-unsaturated acids and derivatives.