Search results for "MOLECULE"
showing 10 items of 5162 documents
Reaktion von elektronenreichen Heterocyclen mit Orthocarbonsäure-Derivaten, 12. Formylierung von Vinylindolen mit Diethoxycarbenium-tetrafluoroborat
1988
Reactions of Electron-Rich Heterocycles with Orthocarboxylic Acid Derivatives, 12. – Formylation of Vinylindoles with Diethoxycarbenium Tetrafluoroborate 2- and 3-vinylindoles 1, 3 are formylated with diethoxycarbenium tetrafluoroborate regioselectively. The significant selectivity and reactivity of formylation of diethoxycarbenium ion in comparison with other thermodynamically more stable dialkoxycarbenium ions are compatible with the known results of hetaryl functionalisation with orthocarboxylic acid derivatives.
A novel and selective fluoride opening of aziridines by XtalFluor-E. synthesis of fluorinated diamino acid derivatives.
2015
The selective introduction of fluorine onto the skeleton of an aminocyclopentane or cyclohexane carboxylate has been developed through a novel and efficient fluoride opening of an activated aziridine ring with XtalFluor-E. The reaction proceeded through a stereoselective aziridination of the olefinic bond of a bicyclic lactam and regioselective aziridine ring opening with difluorosulfiliminium tetrafluoroborate with the neighboring group assistance of the sulfonamide moiety to yield fluorinated diamino acid derivatives. The method based on the selective aziridine opening by fluoride has been generalized to afford access to mono- or bicyclic fluorinated substances.
Anion-π Interaction: An Influential Force in Solid State Molecular Microstructures
2013
The crystal structures of simple triphenyl(pentafluorobenzyl)phosphonium salts provide crucial data on the influence of anion size on the molecular structure of bis(pentafluorobenzyl)phosphonium cations containing two adjacent electron-deficient moieties. Whereas the bromide anions interact by anion-π interaction in a 1:1 mode with the pentafluorobenzene unit Z-configured, the bulkier anions iodide, tetrafluoroborate, and hexafluorophosphate result in a 1:2 tweezer-like anti-configuration in which one anion interacts simultaneously with two pentafluorobenzene units. When spatial separation of the two electron-deficient rings match the size of the anion, anion-π interactions induce a conform…
N-(tert-butoxycarbonylglycyl-alpha,beta-dehydrophenylalanylglycylphenylalanyl)-4-nitroaniline.
2000
In the crystal structure of the tetrapeptide Boc0–Gly1–ΔPhe2–Gly3–Phe4–p-NA (p-NA is para-nitroaniline), C33H36N6O8, there are two independent molecules differing in conformation in the asymmetric part of the unit cell. All the amino acids in the peptide are linked trans to each other. The torsion angles in the main chain of both molecules are close to the values of the type β-II turn. Two intramolecular and three intermolecular N—H⋯O hydrogen bonds stabilize the conformation of each of the molecules.
Computer simulations of undercooled fluids and the glass transition
2000
Abstract Two model studies are presented that attempt to describe the static and dynamic properties of glass-forming fluids via molecular dynamics simulations: The first model is an atomistically realistic model of SiO 2 , the second model provides a coarse-grained description of polymer liquids, i.e., typical `fragile' glassformers, while SiO 2 is the prototype of a `strong glassformer'. For both models, attention is given to the questions as to which range of temperatures are properties in equilibrium, and whether such simulations can help to interpret experiments and/or check theoretical predictions. While in the simulation of SiO 2 using the potential of van Beest, Kramer and van Santen…
Thermogravimetric and calorimetric studies of water absorbed in polyaniline
1995
Abstract Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to study the behavior of residual water absorbed by an emeraldine base and a salt of chemically synthesized polyaniline (PANI—EB, PANI-ES). The matrix of PANI is shown to contain water molecules participating in both reversible and irreversible absorption. In its turn, the reversibly absorbed water consists of two components. The first component (WD 1 ) amounts to 5–7 wt.% and is removable from PANI-EB in a flow of dry nitrogen at room temperature. The second one (6–8 wt.%) of more strongly bonded water (WD 2 ) can be withdrawn from PANI-EB at temperatures from 70 to 150 °C depending on the measu…
Synthesis, structure, physicochemical characterization and theoretical evaluation of non-covalent interaction energy of a polymeric copper(II)-hydraz…
2019
Abstract One dimensional polymeric copper-hydrazone complex {[Cu(H0.5L)(µ1,3-SCN)]0.5ClO4·0.5MeOH}n (1) has been synthesized with Cu(ClO4)2·xH2O and N'-(1-(pyridin-2-yl)ethylidene)acetohydrazide (HL) in presence of NaSCN. The ligand and the complex have been characterized by several spectroscopic techniques (IR, UV–Vis and EPR), cyclic voltammetry and the structure of 1 has been determined by single crystal X-ray diffraction. The complex is an infinite one dimensional polymer bridged by thiocyanate. The magneto-structural correlation has been determined and the non-covalent interactions present in the molecule have been energetically evaluated by means of DFT calculations.
Uranyl Complexes of Alkyl-Bridged Ditopic Diaminotetraphenol Ligands and Their Use as Uranyl Ion Extractors
2013
The coordination chemistry of uranyl ions was studied using long n-alkyl chain (n = 5-8) bridged by N,N,N',N'-tetrakis(2-hydroxy-3-methyl-5-tert-butylbenzyl)diaminoalkanes (H4L1-H4L4) as ligands. All ligands formed 2:1 (U-to-L ratio) complexes with uranyl ions, but in addition 1:1 complexes could be characterized using ligands H4L2 and H4L3. The complexes were characterized by elemental analysis, spectroscopy (IR and NMR), and X-ray diffraction. The 2:1 complexes are of two types: [(UO2)2(H2Lm)(NO3)2(solvent)2] (m = 1 and 2; solvent = ethanol or propanol) or (cation)2[(UO2)2(H2Lm)(NO3)2(anion)2]·xsolvent (m = 2 and 4; cation = triethylammonium, anion = nitrate or thiocyanate, and solvent = …
Syntheses, crystal structures and magnetic properties of mono- and polynuclear [bis(2-arylcarbonyl)amidate]copper(II) complexes
2008
Abstract Five copper(II) complexes of formulas [Cu(bpcam)(CN)(H2O)] (1), [Cu(bpcam)(N3)(H2O)]2 (2), [Cu(bpcam)(NCS)(H2O)] (3), [Cu(bpcam)(dca)(H2O)]2 (4) and [Cu(bpca)(tcm)]n (5) [bpcam = bis(2-pyrimidylcarbonyl)amidate, bpca = bis(2-pyridylcarbonyl)amidate, dca = dicyanamide and tcm = tricyanomethanide] have been prepared and their structures determined by single crystal X-ray diffraction. Compounds 1 and 3 are mononuclear species where each copper atom is five coordinated with a tridentate bpcam and a terminally bound cyanide (1)/thiocyanate (3) ligands creating a basal plane with a water molecule in the axial position of a distorted square pyramid. Compound 2 is made of neutral di-μ-1,1-…
Observation of Very Narrow Linewidths in the Fluorescence Excitation Spectra of Single Conjugated Polymer Chains at 1.2 K
2007
Fluorescence emission and excitation spectra of single poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] polymer molecules embedded in poly(methylmethacrylate) have been recorded at 1.2 K. The ubiquitous spectral diffusion causes large variations in the spectral shape and apparent linewidth in the emission spectra. Nevertheless, we find very narrow (approximately 0.1 cm(-1)) purely electronic zero-phonon lines in the excitation spectra, which are 2 orders of magnitude smaller than previous estimates of the homogeneous linewidth. These results complement the molecular description of the low energy transitions in conjugated polymers.