Synthesis and thermal properties of liquid crystal trimers comprising cyanobiphenyl and salicylaldimine anisometric segments
摘要:
The synthesis and mesomorphism of a series of liquid crystal trimers made by covalently linking two cyanobiphenyl moieties with a central salicylaldimine core through two flexible spacers are reported. Nine different oxyalkyleneoxy spacers varying in the number of carbon atoms and thus, methylene units from 3 to 11 were used to understand structure-mesomorphic property correlations. The optical microscope and differential scanning calorimeter were employed to evaluate their phase transitional behavior. All the trimers exhibit an enantiotropic uniaxial nematic phase over a wide thermal range (>80 degrees C) while a homolog comprising an octamethylene (even-parity) spacer displays, additionally, a metastable smectic phase. The nematic-isotropic transition temperatures critically depend on the parity of the spacer with the values for the odd-parity spacer containing homologs being lower than those of the even members, a feature generally observed in oligomesogens. (C) 2009 Elsevier Ltd. All rights reserved.
Synthesis and thermal properties of liquid crystal trimers comprising cyanobiphenyl and salicylaldimine anisometric segments
摘要:
The synthesis and mesomorphism of a series of liquid crystal trimers made by covalently linking two cyanobiphenyl moieties with a central salicylaldimine core through two flexible spacers are reported. Nine different oxyalkyleneoxy spacers varying in the number of carbon atoms and thus, methylene units from 3 to 11 were used to understand structure-mesomorphic property correlations. The optical microscope and differential scanning calorimeter were employed to evaluate their phase transitional behavior. All the trimers exhibit an enantiotropic uniaxial nematic phase over a wide thermal range (>80 degrees C) while a homolog comprising an octamethylene (even-parity) spacer displays, additionally, a metastable smectic phase. The nematic-isotropic transition temperatures critically depend on the parity of the spacer with the values for the odd-parity spacer containing homologs being lower than those of the even members, a feature generally observed in oligomesogens. (C) 2009 Elsevier Ltd. All rights reserved.
Four-Coordinate Dimethylgallium Compounds Vary in Stability toward Hydrolysis
作者:Robert W. Chesnut、Richard R. Cesati、Cathy S. Cutler、Sara L. Pluth、John A. Katzenellenbogen
DOI:10.1021/om980413x
日期:1998.10.1
oxygen−oxygen, oxygen−nitrogen, and sulfur−nitrogendonor atoms, were prepared from the ligand and dimethylgallium hydroxide; they were characterized spectroscopically and, in two cases, by X-ray crystallography. The percentage decomplexation of the stable (CH3)2Ga+ unit from the Lewis base when exposed to 1000 equiv of water in acetone-d6, determined by 1H NMR, was used as a measure of the relative hydrolytic
通过氢氧化二甲基镓与双齿路易斯碱反应制备四配位的二甲基镓配合物,并评估其在水中分解的稳定性,这是确定其作为放射性药物(尤其是针对特定受体蛋白的药物)潜在用途的关键特性。由配体和氢氧化二甲基镓制备了六种结构类型的模型化合物,其中含有带有氧-氧,氧-氮和硫-氮供体原子的双齿配体。它们通过光谱学表征,在两种情况下通过X射线晶体学表征。稳定的百分比解络(CH 3)2镓+时在丙酮暴露于1000当量的水从路易斯碱部d通过1 H NMR测定的图6用作每种化合物的相对水解稳定性的量度。在我们研究的化合物中,在这些条件下的水解百分比为10%至100%,最水解稳定的化合物被证明是基于N-烷基水杨基醛二酸酯供体的那些。
Synthesis and thermal properties of liquid crystal trimers comprising cyanobiphenyl and salicylaldimine anisometric segments
作者:Channabasaveshwar V. Yelamaggad、V. Padmini Tamilenthi
DOI:10.1016/j.tet.2009.05.076
日期:2009.8
The synthesis and mesomorphism of a series of liquid crystal trimers made by covalently linking two cyanobiphenyl moieties with a central salicylaldimine core through two flexible spacers are reported. Nine different oxyalkyleneoxy spacers varying in the number of carbon atoms and thus, methylene units from 3 to 11 were used to understand structure-mesomorphic property correlations. The optical microscope and differential scanning calorimeter were employed to evaluate their phase transitional behavior. All the trimers exhibit an enantiotropic uniaxial nematic phase over a wide thermal range (>80 degrees C) while a homolog comprising an octamethylene (even-parity) spacer displays, additionally, a metastable smectic phase. The nematic-isotropic transition temperatures critically depend on the parity of the spacer with the values for the odd-parity spacer containing homologs being lower than those of the even members, a feature generally observed in oligomesogens. (C) 2009 Elsevier Ltd. All rights reserved.