Phasmidic compound

Note 3 In some cases the discotic nematic mesophase is formed by compounds that do not have molecules of discotic shape (for example, phasmidic compounds, salt-like materials and oligosaccharides). 

Table 40. Transition temperatures of phasmidic compounds (by courtesy of Malthete et al. [21]).

To date, the crystal structures of more than 200 mesogenic compounds are known. In this review, we wish to present a general overview of the crystal structures of mesogenic compounds up to the end of 1997. Unfortunately, it is not possible to consider the crystal structure determinations of carbohydrate liquid crystals [13, 14], metallomesogens [15-18], phasmid and biforked mesogens [19-22], perfluorinated mesogenic compounds [23-27], benzoic acids [6, 28-31], cinnamic acids [7, 32, 33], dicarboxylic acids [34, 35], cinnamate compounds [8, 36-40], and discotic liquid crystals [41-43] due to the lack of space. 

Fig, 18a,b, The polymorphic behaviour of the phasmidic-like mesogens a molecular model with six terminal chains b phase diagram for the binary mixture of double swallow-tailed compound (I) with conventional rod-like mesogen (II) (adapted from Letko et al. [123])... 

On the other hand, the defensive secretions of Sipyloidea sipylus and of Megacrania tsudai, two phasmid insects originating from Asia, contain volatile compounds, and, in both cases, the whole secretion has a repellent activity [180,181]. 

Thus far no sex pheromone has been described in the Phasmida. Some phasmids produce toxic monoterpenes in typical Class III integumentary glands located behind the head (e.g. Happ et al., 1966). The glands exhibit lipid reserves, carboxylic esterases, phosphatases, alcohol dehydrogenase, and a mevalonate kinase, all of which are suggested to be involved in the production of the toxic compounds (Happ et al., 1966). 

Fig. 6.1.5. (a) Hexa-n-alkoxy terepthal-fe -(4-benzoyloxyaniline) and (Jb) the structure of the hexagonal columnar mesophase formed by this compound. The mesophase has been described as phasmidic . (Malthete, Levelut and Tinh. )... 

The few pentacatenar compounds that have been described in the literature all exhibit columnar (phasmidic) phases [21]. Typical examples of hexacatenar materials are presented in Table 40 [21], Despite their similarity of having five benzene rings in the... 

Compounds 5 were generally recrystallized from absolute ethanol. For different symmetrical phasmids and biforked mesogens, the synthetic route is similar with protected and deprotected phenols or anilines. The central ring moiety is often terephthal-ic acid, 1,4-cyclohexanedicarboxylic acid, or terephthaldehyde. With non-symmetric polycatenar mesogens, the different intermediate compounds are protected or deprotected phenols, anilines and acids or aldehydes. The same method is repeated to add a benzoate. The last step is often an esterification reaction (Scheme 2) unlike the imine derivatives, compounds with ester linkages can be easily purified by chromatography on silica gel with dichloromethane as eluent. 

Other liquid crystal phases composed of molecules having unusual molecular shapes are also known. Some compounds form a cone or bowl shape. These materials are often referred to as bowlic, and some typical examples are hexasubstituted tribenzocyclonones and aza-crowns (17), molecules of which stack on top of each other to form an ordered column which may have anomalous electrical conductivity. When a disklike molecule is divided by a rod-shaped spacer, the molecule (18) is referred to as a phasmid. It exhibits phases bearing some resemblance to columnar discotics. 

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