Synthesis and spatial structure of new chiral dopants from allobetuline series for cholesteric liquid-crystal compositions

New series of chiral dopants for cholesteric liquid-crystal compositions were synthesized on the base of 2-substituted allobetuline derivatives, and their steric structure was determined by X-ray analysis. The relationship between spatial structure of these compounds and their ability to induce cholesteric helix in 4-pentyl-4'-cyanobiphenyl nematic solvent was examined. The highest values of the helical twisting power |beta| (71.38 +/- A 3.4) and (84.25 +/- A 3.7) mkm(-1) mol center dot pats(-1) showed (E)-2-(4-chlorophenylmethylidene)-allobetuline and (2R,3R)-3-(4'-chlorophenyl)-2,2'-spiro-oxyranoallobetuline correspondingly. How the value of |beta| in this series of compounds varies depending on the spatial arrangement relative to the aryl moiety of the chiral core is shown.