Helical Hydrocarbons, saturated

Compound 16, prepared to test the hypothesis that chiral, unfunctionalised and completely saturated hydrocarbons can show optical activity if sufficiently rigid, was found to have a remarkably high specific rotation ([a]j 5 = —648.2), which the authors attribute to the helical arrangement of the compounds with similarly large optical rotations due to a helical arrangement of their 71-bond backbone [18]. 

Helical conformations have been observed in polymethylene, the epitome of a long saturated hydrocarbon. Insofar as a helical structure brings distant atoms closer together than in an extended linear conformation, attractive steric interactions offer an enthalpic contribution towards an explanation of this helicity. 

To construct helical columns several studies have used a different strategy where the core structure is dissymmetric. Saturated mesogens that are derived from chiral saccharides [80,81] and inositols [82] have a core that is chiral and are substituted with hydrocarbon chains. These materials stack into columnar structures but do not show any macroscopic manifestation of the core chirality. This is likely due to poor chiral information transfer from members of the stack. 

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