Kayako Hori

CRYSTAL STRUCTURES OF 4-CYANO-4'-HEXYLBIPHENYL (6CB) AND 4-CYANO-4'-HEPTYLBIPHENYL (7CB) IN RELATION TO ODD-EVEN EFFECTS

Crystal structures of 4-cyano-4-hexylbiphenyl (6CB) and 4-cyano-4-heptylbiphenyl (7CB) with low melting points (13.5 and 30 C, respectively) have been determined at 73 and 33 C, respectively, and compared with previously reported structures of other homologues (n = 2-5, 8-11). In the crystal of 7CB, chains and cores stack alternately, where core regions are largely overlapped with distances of 3.575(2) and 3.597(2)A for N (in CN)... C (in phenyl), showing almost the same packing mode as those of 9CB and 11CB. In the crystal of 6CB, CN groups are antiparallel between neighbouring molecules though the interatomic distances are much longer N... C, 3.673(3) and 3.563(3)A than in 8CB and 10CB (3.28-3.43A), resulting in a quite different packing mode from those of 8CB and 10CB, which had been found to be similar, with CN-CN interactions. Systematic comparison of the homologous series (n = 2-11) reveals odd-even effects, CN-phenyl and CN-CN interactions for odd and even members, respectively, in the crystal stru...

Crystal Structures of 6OCB and 7OCB

Abstract Crystal structures of title compounds have been determined by single crystal x-ray analysis. Crystal data. 4′-Hexyloxy-4-cyanobiphenyl (6OCB), Molecular structures in both crystals are very similar with twisted biphenyl moieties and fully extended paraffin chains. Dimers are formed by close contacts of CN groups between neighboring molecules (C-N: 3.56 and 3.40 A for 6OCB and 3.55 and 3.39 A for 7OCB). The neighboring dimers in 6OCB are overlapped half-and-half, while those in 7OCB are arranged in a smectic-like layer structure.

A Comparative Study on Chiral and Racemic 12-Hydroxyoctadecanoic Acids in the Solutions and Aggregation States: Does the Racemic Form Really Form a Gel?

Chiral and racemic forms of the title compound (12HOAs) were reinvestigated. Gels formed separately from D - and L -12HOAs became a solution containing crystallites on maintaining contact, confirming that DL-12HOA forms no gel, contrary to several reports published over more than ten years, which stated that DL-12HOA formed a gel (for example, P. Terech et al., Langmuir 1994, 10, 3406). The powder X-ray diffraction pattern of D -12HOA was different from that of DL -12HOA and the simulated patterns of two crystal structures of DL-12HOA. 13 C NMR spectroscopy for solutions of C 6 D 6 showed significant difference in the concentration dependence of the low-field shifts at the carboxyl C due to hydrogen-bond formation. Analysis based on multiple equilibria among monomer, dimer, and tetramer was successfully applied to the behavior of D -12HOA, but not to that of DL-12HOA. For DL -12HOA, a modified model including hexamer was applied. It is concluded that association of dimers to tetramers and higher aggregates is more favorable in the DL -12HOA solution than in the D -12HOA solution and that D - and L -12HOA molecules recognize each other even in a dilute solution (lower than 2 mmol L ―1 ) of DL-12HOA. Different NMR spectra were also observed in the solid state.

Angular Dependence of Selective Reflection from the Chiral Smectic C Phase

Abstract Transmission spectra were measured with obliquely incident light for a chiral smectic C phase of (+)-4-n-hexyloxyphenyl 4−(2″-methyl-butyl)biphenyl 4′-carboxylate. Extra reflection bands were observed at about twice the wavelengths of the “normal” Bragg reflection bands, which had been previously predicted by the computor calculation by Berreman.

Crystalline polymorphs of higher homologues of 4-alkoxy-4-cyanobiphenyl, nOCB (n=8,9,10 and 12)

Phase transition behaviour was studied for the crystalline polymorphs of 4-alkoxy-4-cyanobiphenyl, n OCB (n=8,9,10 and 12), by means of differential scanning calorimetry (DSC). The square-plate crystal form, which is composed of distinct smectic-like bilayers with infinite networks of closely arranged CN groups, appears generally for n>7. It is a metastable phase for n=7 and 8. In addition to the square-plate crystal, 8OCB has needle and parallelepiped crystal forms, which are metastable, and the most stable crystalline phase found in a commercially available powder specimen. The parallelepiped crystal shows three competitive processes depending on heating rate: (1) gradual stabilization to the most stable crystalline phase, even at room temperature, (2) transformation to the needle crystal, and (3) direct transformation to the smectic A phase. On the other hand, the square-plate crystal is stable at room temperature and transforms to another crystalline phase, which is supercooled in the commercially ava...

Two Crystal Forms of 4'-octyloxy-4-cyanobiphenyl (8OCB)

Four crystalline phases were found for 4′-octyloxy-4-cyanobiphenyl, C21H25NO. These were square-plate, needle and long parallelepiped crystals, which are all metastable, and a phase found in a commercially available powder specimen, which was the most stable. The structures of the needle and long parallelepiped crystals have been determined at room temperature and 243 K, respectively.

Intermolecular interaction revealed in the crystal structures of chiral smectogenic biphenyl esters

Abstract Intermolecular interactions revealed in the crystal structures are discussed in terms of the lateral overlapping of the core moities and the arrangements of the polar groups for chiral smectogenic biphenyl esters. It is found that the packing modes of the molecules within a layer, which are closely related to the liquid crystal phase sequences, are dependent on the length of the moiety sandwiched by the two polar groups.

The effect of fluorination (2): dependence of alkyl chain length on the crystal structures of mesogenic alkyl 4-[2-(perfluorohexyl)ethoxy]benzoates

The crystal structures of a series of alkyl 4-[2-(perfluorohexyl) ethoxy] benzoates have been studied, with varying numbers of carbon atoms, n, in the alkyl chain. When n = 1 the perfluoroalkyl and alkyl chains were found to aggregate separately from one other, but when n = 5, 6 or 9 the chains aggregated alternately. An intermediate type, of separate and alternate types of packing, was observed when n = 4. Powder X-ray diffraction results strongly suggested that when n = 12 the alternate type of packing was again present, even though the length of the alkyl chain was then twice that of the perfluoro chain; when n = 9 this ratio was 1.5. These features are similar to those observed previously for the octyl analogues, with the exception of the member of the octyl series in which n = 11 and the ratio of alkyl to perfluoro chains was 1.4, for which the separate type of packing was observed. It is concluded that in the hexyl series the alternate type of packing gives sufficient stabilisation of the members with longer chains.

Crystal structures of antiferroelectric mesogen, 4-[(s)-1-methylpentyloxycarbonyl]phenyl 4'-octyl-oxybiphenyl-4-carboxylate and ferroelectric mesogen, 4-[(s)-1-methylhexyloxycarbonyl]phenyl 4'-octyloxybiphenyl-4-carboxylate

Abstract Crystal structures of the title compounds have been determined by X-ray single crystal analysis. The structures are isomorphous with the previously determined structure of MHPOBC, the heptyl homologue.

Crystal structures of ferro- and antiferroelectric mesogens with a 1-methylalkoxycarbonyl group

Abstract Crystal structures have been determined for 4-[(S)-1-methylpentyloxycarbonyl]phenyl, 4-([S)-1-methylhexyloxycarbonyl]phenyl 4′-octyloxybiphenyl-4-carboxylates (1 and 2, respectively) and (R)-1-methylheptyl 4-(4′-octyloxybiphenyl-4-yloxymethylene)benzoate (3), which have SCA ∗, SC∗ and SCA ∗ phases, respectively. All the crystals have a common packing mode with the previously determined structure of 4-(1-methylheptyloxycarbonyl)phenyl 4′-octyloxybiphenyl-4-carboxylate (MHPOBC). Each crystal forms a smectic-like layer structure composed of largely bent molecules with the long alkyl chain of the chiral group almost perpendicular to the core moiety. Differential scanning calorimetry showed that the crystals of 1, 2, and MHPOBC, which have a carbonyloxy group as the central linkage between the biphenyl and phenylene moieties, transform to higher temperature solid phases in a similar temperature range (around 60°C). For 3, which has an oxymethylene linkage between the biphenyl and phenylene moieties, t...