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1.
Mukesh Mishra Roman S. Dabrowski Jagdish K. Vij Avneesh Mishra 《Liquid crystals》2013,40(11):1580-1590
Thermodynamical, dielectric, optical and electro-optical characterisation of pure 8CB and its composites with gold and silver nanoparticles have been studied. Thermodynamical studies suggest a decrease in clearing temperature of the nanocomposite systems as compared to the pure system. Dielectric parameters of pure nematic liquid crystal and nanocomposites in the homeotropic and planar aligned samples have been measured in the frequency range of 1–35 MHz. Ionic conductivity increases significantly in nematic and smectic Ad (SmAd) phases, whereas dielectric anisotropy is almost unchanged for both the nanocomposites. Threshold voltage for Freederick transition, switching voltage and splay elastic constant have decreased in the case of nanocomposite systems. Relaxation frequency and activation energy of an observed relaxation mode corresponding to molecular rotation about the short axis increase in the SmAd phases of both the nanocomposites. The optical study suggests that due to dispersion of nanoparticles, the optical band gap has decreased. 相似文献
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Marinova P. Marinov M. Kazakova M. Feodorova Y. Blazheva D. Slavchev A. Sbirkova-Dimitrova H. Sarafian V. Stoyanov N. 《Russian Journal of General Chemistry》2021,91(5):939-946
Russian Journal of General Chemistry - The presented study is devoted to the structural and biological properties of four derivatives of fluorenylspirohydantoin based on experimental data. The... 相似文献
3.
Suk-Ku Kang Hyun-Sung Cho Hyeong-Su Sim Beon-Kyu Kim 《Journal of carbohydrate chemistry》2013,32(6):807-812
Abstract In connection with our projects on the synthesis of biologically active 5-hydroxyalkan-4-olides which have a chiral 2.3-diol unit,1 we have carried out the synthesis of (4R,5S)-(?)- and (4R,5S)-(+)-L-factors (1).2 the proposed autoregulators from Streptomyees griseus, and muricatacin (2),3 a biologically active constituent from the seeds of Annona muricata L. via 2.3-dihydroxy aldehydes derived from D-glucose. Hex-3-enofuranose4 was prepared by the elimination of thetriflate derived from D-glucose. 相似文献
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Rajib Nandi Hemant Kumar Singh Sachin Kumar Singh D. S. Shankar Rao S. Krishna Prasad Bachcha Singh 《Liquid crystals》2017,44(7):1185-1193
A new polar calamitic liquid crystal, methyl 4-(4?-(4?-(decyloxy)benzyloxy) benzylideneamino)benzoate (M3BA) containing ether and Schiff base groups as linker with terminal polar ester group, has been synthesised and mesomorphic properties are studied by differential scanning calorimetry, polarising optical microscopy, density functional theory, temperature-dependent X-ray diffraction and temperature-dependent micro- Raman study. The smectic A (SmA) mesophase with focal conic texture has been observed with wide mesomorphic range. Layer thickness in SmA phase is greater than the optimised length of the molecule, indicating partially bilayer SmA phase. Analysis of Raman marker bands of C–H in-plane bending of phenyl rings, C=C stretching of rings, C=N stretching and C=O stretching shows structural changes at molecular level at Cr → SmA phase transition and provides proper intermolecular interactions responsible for dimeric unit in partially bilayer SmA phase. 相似文献
5.
《Tetrahedron: Asymmetry》2000,11(23):4681-4686
A short and efficient synthesis of the title compounds is described. (S)-(−)-β-Cuparenone was prepared in 31% yield from p-tolualdehyde and mesityl oxide in eight steps. Absolute stereochemistry was established by means of a diastereoselective cyclopropanation using (R,R)-hydrobenzoin as a recoverable auxiliary. 相似文献
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Shuhei Fujimura Yasuhisa Yamamura Mafumi Hishida Shigenori Nagatomo 《Liquid crystals》2013,40(7):927-932
The appearance of reentrant nematic phase was identified in nCB/8CB (n = 1–6) binary mixtures using differential scanning calorimetry, small-angle X-ray diffraction and polarising microscopy with photomonitor. Phase diagrams can roughly be unified if plotted against the average number of alkyl chain length. Distinction was recognised for the phase boundaries between nematic and smectic A phases of even and odd n of the minor component nCB. The character of 8CB as ‘SmA former’ is briefly discussed. 相似文献
8.
Acetalscanbesynthesizedinanumberofways.Themainproblemintheacetalformationinacidicmediumistoshifttheequilibriumtotherightbyremovalofthewaterformedduringthereactionl.Wesynthesized(2R,4S,SS)-( )-threo-5-(2,2-dich(4-nitrophenyl)-2-aryl-1,3-dioxanesbyacet... 相似文献
9.
This article describes the preparation and liquid crystalline properties of a new homologous series of 4-(4-bromopropyloxy)-4’- (4-alkyloxybenzylidene)anilines in which the phenyl ring is armed by a bromopropyloxy chain.The thermal behavior and mesomorphic properties of the synthesized compounds were studied with particular attention given to the correlation between their phase transition temperatures and anisotropic change influenced by molecular structure.All the members displayed enantiotropic smectic phase except for the homologue with the longest alkyloxy chain(R = C18H37),exhibiting only monotropic characteristic. The presence of bromine atom from the propyloxy side chain is found to be capable of altering and influencing the mesomorphic properties. 相似文献
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Abstract The synthesis and characterization of polymethacrylates, polyacrylates, and poly(methylsiloxane)s containing 4-[S(-)-2-methyl-1-butoxy]-4′-(ω-alkanyl-1-oxy)-α-methylstilbene side groups with ω-alkanyl from 11-undecanyl to 2-ethyl are presented. According to both differential scanning calorimetry and thermal optical polarized microscopy analyses, the poly(methylsiloxane)s containing 1-octyl and 1-hexyl as ω-alkanyl groups exhibit enantiotropic S A and S C* mesophases. All other polymers display only an enantiotropic S A mesophase. 相似文献
13.
《Tetrahedron: Asymmetry》2000,11(20):4221-4225
The resolution of the 4-acetyl[2.2]paracyclophane by the SAMP-hydrazone method is described. A new, short, high yield synthesis of both enantiomers (S)-(+)- and (R)-(−)-4-ethenyl[2.2]paracyclophane is reported. 相似文献
14.
Suitably functionalized alkylphenylsulfones have been used as building blocks for the synthesis of several modified side-chains steroids1. We describe here the synthesis of (S)-2-methyl and (2S)-2,3-dimethyl butyl phenylsulfones (4a) and (6), which can be used for the construction of the side chain of a few marine sterols2 or brassinosteroids3 as well. 相似文献
15.
A novel, efficient and protecting group free enantioselective synthetic approach of (?)-(R)-1 and (+)-(S)-rolipram 2 is described employing the organocatalyzed asymmetric Michael addition, Henry condensation, Wittig olefination and reductive lactamization reactions as key steps. 相似文献
16.
Dr. Alain Carpy Jean -Michel Léger Danielle Roche Michel P. Madesclaire Pascale Besse Henri Veschambre 《Structural chemistry》1995,6(3):191-195
The X-ray crystal structures of (–)-syn-4-phenyl-3-bromo-2-butyl camphanate (I) and (+-anti-4-phenyl-3-bromo-2-butyl camphanate (II) have been determined. Thesyn diastereoisomer of bromohydrin has the (2S,3S) absolute configuration whereas theanti diastereoisomer has the (2S,3R) absolute configuration. The crystallized derivatives I and II have been obtained by the reaction of each stereoisomer of bromohydrin, synthesized by reduction with baker's yeast, with (1S)-camphanic chloride. Crystal data: (I) C20H25BrO4:M
w: 409.32; orthorhombic,P212121;a=11.245(3),b=12.086(1),c=14.512(4) å; Z=4; finalR=0.053 for 1819 observed reflections. (II) C20H25BrO4;M
w=409.32; monoclinic, P21;a=11.352(1),b=6.378(1),c=14.255(2) å,=110.38(1);Z=2; finalR=0.045 for 1672 observed reflections. 相似文献
17.
价廉易得的L-亮氨酸先以苄基同时保护氨基及羧基得(S)-2-(二苄胺基)-4-甲基戊酸苄酯,进而在碱性条件下与乙腈发生亲核取代反应得(S)-4-(二苄胺基)-6-甲基-3-氧代庚腈,再经硼氢化钠选择性还原羰基得(3S,4S)-4-(二苄胺基)-3-羟基-6-甲基庚腈,用双氧水氧化得(3S,4S)-4-(二苄胺基)-3-羟基-6-甲基庚酸,最后在Pd(OH)2/C-H2作用下脱掉苄基得到(3S,4S)-4-氨基-3-羟基-6-甲基庚酸,即(3S,4S)-statine。整个合成路线总产率为33.6%。 相似文献
18.
《Tetrahedron: Asymmetry》1998,9(4):653-656
Treatment of 4-bromo[2.2]paracyclophane with n-butyllithium followed by CO2 produced [2.2]paracyclophane-4-carboxylic acid, 1. Both enantiomeric forms [63% of (+)-(S)-1 and 48% of (−)-(R)-1] were obtained by resolution via the corresponding diastereomeric α-(p-nitrophenylethylammonium salts. 相似文献
19.
以高藜芦胺为起始原料,经N-磺酰化反应制得高藜芦磺酰胺(2);2分别与芳乙烯甲醚经对甲苯磺酸催化的Pictet-Spengler反应后用金属钠脱除Ts基团合成了(±)-norlaudanosine(5a)和(±)-O,O-dimethylcoclaurine(5b);使用半量拆分法,以N-乙酰-L-苯丙氨酸为拆分剂,制得(S)-(-)-5a和(S)-(-)-5b,其结构经1H NMR,13C NMR,IR,MS和HR-ESI-MS确证。 相似文献