X-ray Studies of Biphenylcyclohexanes in the Solid Crystalline and Liquid Crystalline States

Abstract

The crystal and molecular structures of two disubstituted biphenylcyclohexanes (BCHs) of the general formula R—C₆H₁₀C₆H₄—C₆H₄—X were determined (BCH5CN, R: C₅H₁₁ X: CN; a = 12.671(3), b = 5.567(1), c = 28.695(5) Å, β = 97.174(4)°, space group P2 ₁/c. BCH30, R: C₃H₇, X: H, a = 6.839(2), b = 8.219(2), c = 31.159(8) Å, β = 99.63(1)°, space group P2₁/c). Crystal data only is given of BCH52, R: C₅H₁₁ X: C₂H₅; a = 17.09(2), b = 6.79(1), c = 37.34(3) Å, space group Pbcn Refinement leads to R = 0.089 (BCH5CN) and R = 0.128 (BCH30) respectively. In both compounds, the molecules form layers in the crystalline state. The dihedral angles between the phenyl rings in the biphenyl unit are 2.4° (BCH5CN) and 23.8° (BCH30) respectively. X-ray examinations of the smectic states, and also of some additional BCH-compounds (BCH50, R: C₅H₁₁, X: H; BCH54, R: C₅H₁₁, X: C₄H₉; BCH7CN, R: C₇H₁₅, X: CN; BCH5NH₂, R: C₅H₁₁ X: NH₂) give monolayered, crystalline smectic B phases for the nonpolar compounds. The compounds containing the polar cyano-group exhibit partial bilayered structures in the smectic A phase as well as in the nematic phase. The bilayer model is discussed.