2-[4-Alkenyloxy)phenyl]-5-alkylpyrimidines The relationship between position and nature (E/Z) of the double bond and transition temperatures

Abstract

To cite this article: S. M. Kelly (1993) 2-[4-Alkenyloxy)phenyl]-5-alkylpyrimidines The relationship between position and nature (E/Z) of the double bond and transition temperatures, Liquid Crystals, 14:3, 675-698,The 5-n-alkyl-2-[4-(n-alkoxy)phenyl]pyrimidines are essential components of most commercial chiral smectic C mixtures for eiectrooptic display devices based on ferroelectric effects. This is due to their generally relatively low melting points, enantiotropic, relatively wide range smectic C mesophases, low viscosity and ease of preparation. An unsaturated carbon-carbon double bond has now been introduced into the terminal alkoxy chain of the 5-n-alkyl-2-[4-(alkoxy)phenyl]pyrimidines to produce the corresponding alkenyloxy substituted derivatives. The position and nature ( E / Z ) of the double bond has been varied systematically and the effect on the liquid crystal transition temperatures studied. A number of homologous series of the most interesting alkenyloxy substituted materials has been prepared and evaluated. The position and nature ( E / Z ) of the double bond changes the conformation of the alkenyloxy chain substantially. This can result in significantly higher smectic C transition temperatures for compounds with a trans double bond (E) at an even number of carbon atoms from the molecular core. Significantly lower transition temperatures (including the melting point) are observed for materials with a cis double bond ( Z ) at an odd number of carbon atoms from the molecular core. Comparisons with the corresponding alkoxy substituted materials (i.e. without a double bond) are made.

Synthesis of Liquid Crystal Silane‐Functionalized Gold Nanoparticles and Their Effects on the Optical and Electro‐Optic Properties of a Structurally Related Nematic Liquid Crystal

“…Although compounds 3 a and 3 b did not show liquid-crystalline behavior, POM confirmed the formation of the enantiotropic smectic A and nematic phases and the monotropic smectic C phase for LCs 2 a and 2 b with the phase-transition temperatures matching those previously reported [84] (for further experimental details see the Supporting Information). The terminal alkenes of 2 a and 2 b were converted into trimethoxysilane end groups by a hydrosilylation reaction.…”

Formation of Two-Dimensional Mixed Crystals on Graphite Observed by Scanning Tunneling Microscopy

“…Trans unsaturated molecules are essentially the same size as saturated molecules but unsaturation disturbs the regularity of the alkyl chains which can interfere with molecular packing. Cis unsaturation is well-known to cause a large decrease in melting points − and in this system trans unsaturation lowers melting points as well. However, cis or trans unsaturation has only a minor effect on bulk densities, which usually differ by only 1−4% from the corresponding saturated compounds in both liquids and solids.…”

“…The fact that the smaller unit cell was never observed in the mixtures argues against phase separation, especially since the saturated compound seems more likely to crystallize preferentially. This is based on the fact that in 3-D crystals unsaturation lowers melting points by hindering packing [9][10][11] and a similar effect is expected to occur in 2-D crystals. In addition, saturated hydrocarbons on graphite are stabilized by the lattice match between the centers of the graphite rings and the alkyl hydrogens.…”

Large Electroclinic Effect and Associated Properties of Chiral Smectic a Liquid Crystals

“…The next study was therefore aimed at developing new achiral tails for lowering melting points and for broadening the liquid crystal phase ranges. The idea was to incorporate fatty acid-derived tails with cis double bonds to lower the melting points, an approach used successfully in other classes of materials by Kelley [12]. Indeed all these materials (Fig.…”