1,721,003 research outputs found
Interplay between cone and partial-cone geometry in doubly-bridged calix[8]arenes investigated by X-Ray and 2D NMR
No full textCalixcyclitols: a new class of polar hybrid hosts obtained by oxygenation of calixarene phenol rings
No full textThe first examples of hybrid calixarene hosts containing cyclitol moieties (calixcyclitols) have been obtained by treatment with LiAlH4 of diepoxydiol and tetraepoxytetrol calix[4]arene derivatives. A 6-oxabicyclo[3:1:1]heptanetriol or a cyclohexanetetrol ring was obtained depending on the stereochemical features of the diepoxydiol moiety. Preliminary binding studies toward anionic guests showed a discrete selectivity of calixcyclitol 9 vs H2PO4-
Molecular assembly of distal p-H-calix[4]dihydroquinone units
No full textThe solid-state self-assembly properties of distal dimethoxy-p-H-calix[4]dihydroquinone, 3, are described. Three
different crystalline forms were obtained under different crystallization conditions. The cone conformation is maintained in all three crystalline forms, being favored by lower rim hydrogen bond formation. The first crystal, 3A, is constituted by mutual-inclusion calixarene trimers connected to each other by water molecules. The second and third ones (3B and 3C) are formed by alternate layers of crystallographically independent calixarene molecules
A 1,5-DIARYLPYRROLE DERIVATIVE
No full textThe structure of the 1,5-diarylpyrrole derivative, ethyl 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-2-methyl-3-pyrrolecarboxylate, C20H16Cl3NO2, has been determined. The orientation assumed by the phenyl rings corresponds to the deepest of the two minima obtained from ab initio calculations. All bond distances and angles are in the expected ranges
CONFORMATION IN 2,3-DIFLUOROBUTANES
No full textA conformation anal. for meso- and d,l-2,3-difluorobutanes has been carried out, employing 1H and 19F NMR and theor. calcns. The real configurations of the two isomers were assigned by specific optical rotation measurements of the products coming from an optically active precursor. Gauche conformations were predominant for meso (E) isomer, while the d,l (T) isomer showed all possible staggered rotamers almost equally populated. Finally remarks for NMR peak assignment of homo- and copolymers partially fluorinated by using gauche additive effects are given
Oxygenation of calixarene phenol rings
No full textThe first examples of epoxy-p-quinol and diepoxy-p-quinol calixarene derivatives have been obtained by base-promoted direct addition of O-2 (oxygenation) to calixarene phenol rings. The regio- and stereochemistry of these derivatives was determined by 2D NMR studies, in conjunction with MM3 calculations, and X-ray crystallography. Both the oxygenation and the subsequent carbonyl reduction occur with a preferential attack to the less hindered exo face of the calixarene ring
5,5’-Bicalix[4]arene: the prototypal, bridgeless, double calix[4]arene of the head-to-head type
No full textX-Ray crystal structure of a p-hydroxycalix[6]arene derivative
No full textThe first molecular structure of a p-hydroxycalix[6]arene 6 has been determined by a single crystal X-ray diffraction study. The calix[6]arene molecule assumes a 1,2,3-alternate conformation with all OH groups at the upper rim engaged in H-bonds with pyridine molecules. The stacking of molecules of p-hydroxycalix[6]arene 6 along the a and c axes gives rise to a solvent pseudo-cylindrical cavity at the centre of the cell
- …
