Question 25.3: Would the following molecule make a good liquid crystal? Why...
Would the following molecule make a good liquid crystal? Why or why not?
Strategy Cholesteryl benzoate exhibits liquid crystal properties because it has structurally rigid regions (fused rings and sp^2-hybridized carbon atoms) and because it is relatively long compared to its width. Examine the structure in question to see if it has rigid regions and to see if it is longer in one dimension than in another.
Setup Carbon atoms that are sp^2-hybridized contribute to the rigidity of a molecule’s shape.
The left-hand portion of the molecule contains an sp^2-hybridized carbon atom, a benzene ring, anothersp^2-hybridized carbon atom, and another benzene ring. These features are relatively rigid and should allow the molecule to maintain its shape when heated. The chain of \text{CH}_2 groups ending in a \text{CH}_3 group is not rigid due to free rotation about the carbon-carbon single bonds (i.e., sp^2-hybridized carbon atoms). The overall shape of the molecule is longer than it is wide, though, which combined with a large portion that is rigid should make the molecule a good candidate for liquid crystal behavior.