The Synthesis and Transition Temperatures of Some Fluoro-Substituted 4-Cyanophenyl and 4-Cyanobiphenyl-4′-yl 4-Pentyl- and 4-Butoxy-Benzoates

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Abstract
A series of 4-cyanophenyl 4-X-benzoates and a series of 4-cyanobiphenyl-4′-yl 4-X-benzoates (X =pentyl, butoxy) have been prepared without fluoro-substitution and with mono-fluoro to tetra-fluoro-substitution; all possible combinations of substitution patterns at the positions ortho- to the cyano group and ortho- to the carboxylate group have been obtained in an attempt to determine the structural features which are responsible for some members of these series showing very large positive values of dielectric anisotropy. The synthesis of novel precursors required for the preparation of these esters is described and the melting points and transition temperatures of the esters are discussed and an explanation is provided for the variation of TN -1 values with position and extent of fluoro-substitution.