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'Mesophases Sugar SS Dialkyl Acetals' in keywords
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1988 (1)
1Author    Andreas Eckert, Bernd Kohne, Klaus PraefckeRequires cookie*
 Title    Flüssigkristalline Kohlenhydratdithioacetale * * Liquid Crystalline Carbohydrate Dithioacetals*  
 Abstract    Aus Anlaß der vor 100 Jahren vom Botaniker F. Reinitzer [1] und dem Physiker O. Lehmann [2] begonnenen Flüssigkristallforschung [3] Various S,S-dialkyl acetals of hexanal and numerous aldoses, tripodal in structure, have been synthesized, characterized and investigated by optical microscopy and D. S. C. Most of these geminal dithioacetals show a complicated melting behaviour and are thermotropic liquid crystal-line, exhibiting only one smectic-like phase of identical type. This mesophase is not miscible with the S Ad -Phase of other amphiphilic sugar-based liquid crystals. As shown in a homologues series of D-glucose S.S-dialkylacetal derivatives clearing points are rising as function of growing number n of carbon atoms in their S-alkyl chains. With constant n given a similar trend is observed by varying the length of the polar, hydrophilic sugar units. Regarding stereochemistry the dithioderivatives 5 and 12 of the pentose or hexose series, respectively, with a configuration related to that of D-mannose exhibit relatively the most stable mesophase. However, the most stable mesophase of all investigated sugar dithioderivatives is exhibited by the heptose S.S-dialkylacetal 13. Surprisingly, derivative 10 of L-rhamnose (6-desoxy-L-mannose) — the terminal hydroxyl group in the sugar chain of mannose is missing! -showed to be non-mesomorphic, demonstrating that a terminal hydroxyl group of these sugar derivatives seems to be essential for exhibiting a mesophase. On the other hand, as shown with the dithioderivative 9 of 2-desoxy-D-glucose in comparison to the derivative 8e and 12 of D-glucose or D-mannose, respectively, their clearing points seem to be less, although differently effected if an internal hydroxyl group — for instance here at C-2 — has been stripped off. Melting behaviour as well as thermomesogenic properties of the presented amphiphilic carbo-hydrate liquid crystals in relationship to their molecular structure are discussed in detail. 
  Reference    Z. Naturforsch. 43b, 878—888 (1988); eingegangen am 22. Dezember 1987 
  Published    1988 
  Keywords    Aldoses, Liquid Crystals, Mesophases Sugar SS-Dialkyl Acetals, Tripodal Amphiphiles 
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 TEI-XML for    default:Reihe_B/43/ZNB-1988-43b-0878.pdf 
 Identifier    ZNB-1988-43b-0878 
 Volume    43