Configuration of Synthetic Å‘strogens

Abstract

IT has recently been shown¹ by a consideration of the molecular resonance properties associated with various structural models that the observed² centro-symmetrical nature of the hexadiene-Å"strol molecule (ppâ²-dihyaroxy-3 : 4-diphenyl-2 : 4-hexadiene) [I] requires the hexadiene chain to exist in the planar trans-trans-configuration shown below. The two benzene rings are probably rotated by some 50° out of the hexadiene plane in order to reduce the steric interference of the ortho hydrogen atoms. Similar arguments lead to a non-coplanar structure of stilbÅ"strol (ppâ²-dihydroxy-αβ-trans-diethylstilbene [II], in which the conformation of the aliphatic hexene chain must be expected to approximate to a zig-zag shape rather than to the S-form [III], the latter offering much greater steric opposition to the resonance-induced tendency of the stilbene skeleton to attain full coplanarity.