Structure Dependence of Cholesteric Mesophases II

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Abstract
To find a correlation between mesomorphic character and the position of double bonds in ring A, we investigated the octadecanoates of 5α-cholest-1-en-3β-ol and cholest-4-en-3β-ol, neither of which was mesomorphic. We attribute this to a change in polarizability. The influence of chain length and substituents at the 17β-position on the mesomorphic behavior was studied with alkanoates of various substituted androst-5-en-3β-ols. Monotropic cholesteric mesophases were exhibited by the octadecanoates of methyl 3β-hydroxychol-5-en-24-oate and 20β-carbomethoxypregn-5-en-3β-ol, and by methyl 3β-acetoxy-24-norchol-5-en-23-oate. This proves that the 17β-side chain of cholesterol can be shortened considerably without destroying mesomorphic characteristics. However, with the introduction of polar substituents in the 17β-position and simultaneous loss of the optically active center at C-20 cholesteric mesophases could no longer be obtained. The octadecanoates of pregn-5-en-3β-ol-20-one, androst-5-en-3β-ol-17-one, 17β-carbomethoxyandrost-5-en-3β-ol, and androst-5-en-3β, 17β-diol were not mesomorphic.

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