The Crystal and Molecular Structures of Two 4-Alkenyl-substituted Bicyclohexylnitriles

Abstract

The crystal and molecular structures of two mesomorphic alkenyl bicyclohexylnitriles have been studied by single-crystal X-ray diffraction and molecular mechanics. 1-(4′-cyanocyclohexyl)-trans-4-(1-buten-4-yl)-cyclohexane (0d₃CC): monoclinic, P2₁/c; a = 6.415(1), b = 20.453(5), c = 22.998(7) Å, β = 94.99(3)°, V = 3006.0 ų; Z = 8; R = 0.035, R_w = 0.039 for 4509 reflections with I_o ≥ 2[sgrave] (I_o). 1-(4′-cyanocyclohexyl)-trans-4-(2-penten-5-yl)-cyclohexane (1d₃CC): monoclinic, P2₁/n; a = 5.418(1), b = 31.992(7), c = 9.380(2) Å, β = 101.93(2)°, V = 1590.7 ų; Z = 4; R = 0.063, R_w = 0.057 for 1613 reflections with 1_o ≥ 2[sgrave] (I_o). The molecular structures are discussed with regard to the torsional angles around the C(4)‒C(7) bond connecting the cyclohexane ring and the flexible chain in each of the molecules. A scan in the conformational space around the C(4)‒C(7) bond, using the molecular mechanics, program MM2, reveals that the two different conformations, which the two molecules assume in their crystal structures, are energetically equivalent. 0d₃CC shows a parallel imbrication of molecules in the crystal, which yields a nematic mesophase. On the other hand, 1d₃CC displays a herringbone relationship on molecular stacks in the crystal structure, but it still yields a nematic mesophase as well.