Structural Arrangements of the Mesogenic Compounds 4-Ethyl-4′-(4″-pentylcyclohexyl)biphenyl and 4-Ethyl-2 ‘-fluoro-4’ -(4″-pentylcyclo-hexyl)biphenyl (BCH's) in the Crystalline State

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Abstract
The crystal and molecular structures of 4-ethyl-4′-(4″-pentylcyclohexyl)biphenyl (BCH52) and its fluoro derivative, 4-ethyl-2′-fluoro-4′-(4″-pentylcyclohexyl)biphenyl (BCH52F) are described. The crystal data are: a = 31.564(5), b = 5.511(1), c = 25.243(4) Å, 13 = 104.904(4)°, space group C2/c for BCH52 and a 17.156(3), b = 6.792(1), c = 37.334(6) Å, space group Pbcn for BCH52F. The structures refined to R values of 0.0711 (BCH52) and 0.0836 (BCH52F) using 2624 reflections for BCH52 and 2781 reflections for BCH52F. The torsion angles between the phenyl rings are radically different, being 3.9° in BCH52 and 41.9° in BCH52F. The torsion angles between the alkyl, phenyl, and cyclohexyl subunits of the molecules are compared and the influence of the fluoro substitution is discussed. The patterns of packing of the crystal structures are discussed, especially in terms of short-range ordering. Comparisons with similar compounds are made.