| Research Abstract |
(1) Systematic comparison of the crystal structures of two typical mesogenic series, 4'-alkoxy-4-cyanobiphenyls, (nOCB) and 4'-alkyl-4-cyanobiphenyls (nCB), has revealed that a cyano-cyano interaction is dominant in the higher members of nOCB, while nCB shows a remarkable odd-even effect ; cyano-cyano and cyano-phenyl interactions for the even and odd members, respectively. IR wavenumbers of the CN stretching vibrations are 0.5 and 1.0 cm^<-1> higher for nCB than for nOCB in dilute solutions and liquid crystalline phases, respectively. The former is attributable to the different intra-molecular interactions, while the latter, in addition, to the difference in the intermolecular interactions, which are further to the difference in the degree of overlapping of molecules, larger by 3 A for nOCB than for nCB. Similar results were obtained for two series of cyano-esters.
(2) Crystal structures have been determined for two series of dimeric mesogens with two mesogenic cores connected with an alkyl chain, which show remarkable odd-even effects in melting and clearing points. Extended and bow-shaped molecules are arranged with half-and-half overlapping for the even and odd members, respectively, being related to the odd-even effects.
(3) In order to obtain information about intermolecular interactions, crystal structures have been systematically determined for compounds with slightly different molecular configurations but different liquid crystalline behavior, such as a diphenylpyrimidine having a unique isotropic liquid crystalline phase and its isomers with no isotropic mesophases.
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