Stereogenic Motif Consisting of Rigid Ring and Intraannular Chains: Isolation and Structures of Stereoisomers of 9-Alkyl-1,8-anthrylene−Butadiynylene Cyclic Dimers ToyotaShinji OnishiHiroyuki KawaiYoshihiro MorimotoTakaaki MiyaharaHiroaki IwanagaTetsuo WakamatsuKan 2009 Stereoisomers of the title π-conjugated compounds with intraannular propyl and butyl groups were isolated by chromatography. The high barrier to isomerization is attributed to the steric hindrance between the alkyl chains and the rigid framework.