Search results for "ALK"
showing 10 items of 4314 documents
Structure and Dynamics of Liquid Crystalline Polymers from Deuteron NMR
1983
The molecular structures of thermotropic liquid crystalline polymers, which have been synthesized systematically in recent years, are described according to the model of decoupling the molecular motions of the mesogenic groups and the polymer chain by inserting a flexible spacer. The molecular structure is related to the properties of these systems, e.g., phase transition temperatures, mesophases formed, etc. The structure and mobility of a specific side chain, liquid crystalline polyacrylate with phenyl benzoate as a mesogenic group is investigated by deuteron NMR and compared with the behaviour of low molecular weight analogues selectively deuterated at equivalent positions, i.e., at the …
Langmuir-Blodgett Mono- and Multilayer Assemblies of Amphiphilic Liquid- Crystalline n-Alkyl-4′-n-alkoxybiphenyl-4-carboxylates. I
1991
Five n-Alkyl-4′-Alkoxy-biphenyl-4-carboxylates were investigated as Langmuir monolayers at the air/ water interface and as Langmuir-Blodgett (LB) films on solid supports. All five compounds form stable monolayers at the air/water interface and can be transferred onto solid supports yielding LB-films, whose structures and kinetic behavior strongly depend on the headgroup. The structures of the LB-films were investigated by means of optical textures and X-ray diffraction and compared with the structures of the corresponding bulk phases which were investigated by means of Differential Scanning Calorimetry and X-ray powder diffraction. The LB-films of the acid and the two methyl esters exhibit …
Two-Component Hydrogels Formed by Cyclodextrins and Dicationic Imidazolium Salts
2013
In the framework of our recent interest in studying the gelling behaviour of imidazolium salts, we took into account the possibility of obtaining two-component hydrogels by combining cyclodextrins and dicationic imidazolium salts. In particular, we used diimidazolium salts differing in the alkyl chain length and in the size, shape, and coordination ability of the anion, namely the 3,3′-di-n-decyl- and 3,3′-di-n-dodecyl-1,1′-(1,4-phenylenedimethylene)diimidazolium dibromide, and 3,3′-di-n-dodecyl-1,1′-(1,4-phenylenedimethylene)diimidazolium ditetrafluoroborate and dihexafluorophosphate. As far as cyclodextrins are concerned, to gain information on the effects of different sized cyclic oligos…
pH-Dependent ligands as carriers in transport experiments
2004
Abstract Conformationally pH-regulated ligands have been used as carriers in transport experiments. The experiments were carried out through bulky membranes and the pH at the source phase and at the receiving phase were modified to study the ability of ligands to act as pH-regulated carriers. The influence of pH on transport efficiency seems to be related to its influence on conformational equilibrium. X-ray determination of one precursor compound has been useful for determining the stereochemistry of one of the carriers. To cite this article: A.M. Costero et al., C. R. Chimie 7 (2004).
Pauson–Khand reaction of fluorinated compounds
2020
The Pauson–Khand reaction (PKR) is one of the key methods for the construction of cyclopentenone derivatives, which can in turn undergo diverse chemical transformations to yield more complex biologically active molecules. Despite the increasing availability of fluorinated building blocks and methodologies to incorporate fluorine in compounds with biological interest, there have been few significant advances focused on the fluoro-Pauson–Khand reaction, both in the inter- and intramolecular versions. Furthermore, the use of vinyl fluorides as olefinic counterparts had been completely overlooked. In this review, we collect the advances both on the stoichiometric and catalytic intermolecular an…
Nucleophilic benzoylation using lithiated methyl mandelate as a synthetic equivalent of the benzoyl carbanion. Oxidative decarboxylation of α-hydroxy…
2001
Abstract The synthesis of alkyl aryl ketones using lithiated methyl mandelate as a synthetic equivalent of the benzoyl carbanion is reported (Umpolung). The methodology involves alkylation of methyl mandelate, hydrolysis of the ester group and oxidative decarboxylation of the resulting α-hydroxyacids. The last step is carried out in a catalytic aerobic way using a Co(III) complex in the presence of pivalaldehyde under very mild and advantageous conditions. The procedure is also applied to methyl mandelates substituted on the aromatic ring.
Gas chromatography of homologous esters
1984
Abstract The gas chromatographic retention behaviour of the butanoyl and 2-, 3- and 4-chlorobutanoyl esters of C 3 —C 5 saturated aliphatic branched-chain and unsaturated C 3 —C 6 alcohols on SE-30 and OV-351 glass capillary columns operated iso-thermally at several temperatures is reported. Retention index increments at 80, 120 and 160°C show the effects of chain branching and the olefinic and acetylenic unsaturation in the alkyl chain and the effect of the position of the chlorine substituent in the acyl chain. The results are compared with the behaviour of the corresponding n -alkyl esters and the chlorinated propanoyl esters.
Rhodium and palladium complexes from 1,1′ and 1,2 ferrocenylphosphine as bidentate ligands. Versatile coordination
2000
Abstract The complexation of the mixed bidentate ligands 1-diphenylphosphino-1′-diphenylthiophosphinoferrocenyl and 1,2-bis(diphenylphosphino)ferrocenyl with rhodium(I) and palladium(II) species yield a range of mono- and dirhodium or palladium complexes. Their interest as possible catalysts for alkene hydroformylation and alkoxycarbonylation and Heck coupling reactions has been assessed. Fe[C5Me4P(S)Ph2][C5Me4PPh2]PdCl2 and Fe[C5H2-1,2-(PPh2)2-4-tBu][C5H5]PdCl2 have been characterized by single-crystal X-ray diffraction studies.
Syntheses, crystal structures and magnetic properties of five new manganese(ii) complexes: Influence of the conformation of different alkyl/aryl subs…
2014
et al.
Determination of alkylphenol ethoxylates by micellar electrokinetic chromatography with bile salts
2001
Octyl- and nonylphenol ethoxylates (OPEs and NPEs) with different numbers of ethoxy units (average values: n = 10 and N = 40 for OPEs, and n = 10 for NPEs) were separated by micellar electrokinetic chromatography under positive polarity using an 80 mM borate buffer of pH 8.5 containing sodium deoxycholate (SDC) or sodium cholate (SC). When sodium dodecyl sulfate (SDS) was added to the background electrolyte (BGE) in the absence of the bile salt, a single peak at a migration time longer than that of the EOF was obtained. Substituting the SDS by a bile salt, the homologues were resolved. At the same bile salt concentration, resolution between the homologues was higher with SDC than using SC. …