Search results for "Nuclear magnetic resonance spectroscopy"
showing 10 items of 843 documents
Acylated Triterpene Saponins from Atroxima libericaStapf
2011
The four new acylated triterpene saponins 1–4, isolated as two pairs of isomers and named libericosides A1/A2 and B1/B2, one pair of isomers 5/6, the (Z)-isomer libericoside C2 (5) being new, one new sucrose ester, atroximoside (7), and eight known compounds were isolated from the roots of Atroxima liberica by repeated MPLC and VLC on normal and reversed-phase silica gel. Their structures were elucidated on the basis of extensive 1D- and 2D-NMR studies (1H- and 13C-NMR, DEPT, COSY, TOCSY, NOESY, HSQC, and HMBC) and mass spectrometry as 3-O-β-D-glucopyranosylpresenegenin 28-{O-α-L-arabinopyranosyl-(13)-O-β-D-xylopyranosyl-(14)-O-α-L-rhamnopyranosyl-(12)-4-O-[(E)-3,4-dimethoxycinnamoyl]-β-D-f…
The First Examples of a Crown Ether Intramolecularly Encapsulating Mono- and Diorganotin Dications: Synthesis and Structures of [PhSnCH2([16]crown-5)…
2010
The reaction of silver perchlorate with [PhI 2 SnCH 2 ([16]crown-5)] (1) and [I 3 SnCH 2 ([16]crown-5)] (2) gave the organotin(IV)-substituted crown ether complexes [PhSnCH 2 ([16]crown-5)][ClO 4 ] 2 (3) and [HOSnCH 2 ([16]crown-5)][Y] 2 (4: Y= ClO 4 , 5: Y=CF3 S 03 ) , respectively. All compounds have been isolated as air-stable materials and characterised by 1 H, 13 C, 119 Sn and 119 Sn MAS (5) NMR spectroscopy, ESIMS spectrometry, elemental analysis and by single-crystal X-ray diffraction analysis. The molecular structures of 3-5 show that the tin(IV) cation fits perfectly into the crown ether cavity and is coordinated by the five oxygen atoms of the ring to give a pentagonal bipyramidal…
Cyclometallation reactions in complexes of the type Rh(oq)(CO)[P(o-BrC6F4)Ph2]. The molecular structure of F4)Ph2] (oq = 8-hydroxyquinolinate)
1984
Cyclometallation occurs when a solution of the complex Rh(oq)(CO)(PCBr), (PCBr = 2-bromo-3,4,5,6-tetrafluorophenyldiphenylphosphine; oq = 8-hydroxyquinolinate) in toluene is refluxed, giving Rh(oq)2(PC) (PC = P(C6F4)(C6H5)2) and a dimeric compound, not yet completely characterized, formulated as Rh2Br(oq)(PCBr)2. Rh(oq)2(PC) was characterized by elemental analysis, by conductance measurements, and by 19F, 31P NMR and infrared spectroscopy. Its molecular structure was determined by single-crystal X-ray methods and refined by standard procedures to final agreement factors R and Rw of 0.067 and 0.060 for 5346 observed data. Lattice constants are 15.8494(6), 14.7188(5), 14.6675(5) A and β 96.93…
Asymmetrically substituted calix[4]arenes; A two-dimensional 1H NMR study of a tetraester derivative in the cone-conformation
1991
Abstract Several new chiral calix[4]arenes with three or four different substituents in the p-position have been prepared by fragment condensation. Standard derivatization procedures always led to the formation of mixtures of various conformational isomers from which the derivative in the cone-conformation could be isolated only by preparative HPLC. For a tetraester derivative it was shown by two-dimensional 1H NMR spectroscopy, that due to the different substituents the cone-conformation is strongly distorted. The sodium complex of this tetraester, however, assumes a regular cone-conformation again.
Synthesis of ruthenium(II) compounds with ortho-oxypyridinate ligands (hp). Crystal structure characterization of [Ru(η6-p-CH3C6H4CH(CH3)2)Cl(hp)]
1988
Abstract The reaction of [Ru(η6-p-cymene)Cl2]2 (p-cymene = p-CH3C6H4CH(CH3)2) with Nahp in THF yields [Ru(η6]-p-cymene)Cl(hp)] (1). The crystal structure of (1) has been determined by X-ray methods. (1) crystallizes in the space group Pbca, with a = 16.629(2), b = 10.201(3), c = 17.752(2) A. The compound contains one coordinated arene group, one chlorine and one hp group in a chelating coordination mode. The reaction of (1) with Aghp yields [Ru(η6-p-cymene)(hp)2] (2). The 13C NMR spectrum at - 70°C is consistent with a structure Ru(η6-p-cymene)(η2-hp)(η1-hp). At room temperature a rapid interconvertion between the two hp ligands occurs according to the observed 1H and 13C NMR spectra.
A magnetic self-contained thermochromic system with convenient temperature range
2019
A new ionic liquid with sugar-based ligand has been prepared and used to coordinate cobalt(II), at low loading, in an ionic liquid solution. The system obtained reveals magnetic switching and marked thermochromism in solution/polymer films over a convenient temperature range (20–60 °C). This system is self-contained, devoid of any volatile substances, and reproducible over multiple thermal cycles. The colour change can be attributed to a change in the coordination geometry from octahedral (pink) at room temperature to tetrahedral (blue) on warming, monitored by 59Co NMR spectroscopy, which was used for the first time to study the change. This material may find applications in stimuli-respon…
Synthesis of new soluble polybenzyls by Friedel-Crafts reactions
1999
Soluble polybenzyls were prepared by a catalytic electrophilic Friedel-Crafts type polycondensation between α,α'-dichloro-p-xylene and substituted (by an alkyl or an alkoxy side-chain) mesitylene. The influence of the length of the side-chain on the solubility of the polymer was examined. The polymers were found to be soluble in common organic solvents. Polymer characterizations were made by 13 C nuclear magnetic resonance spectroscopy (NMR), size exclusion chromatography (SEC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and elemental analysis.
The effect of silica nanoparticles on the morphology, mechanical properties and thermal degradation kinetics of PMMA
2012
Abstract Silica–PMMA nanocomposites with different silica quantities were prepared by a melt compounding method. The effect of silica amount, in the range 1–5 wt.%, on the morphology, mechanical properties and thermal degradation kinetics of PMMA was investigated by means of transmission electron microscopy (TEM), X-ray diffractometry (XRD), dynamic mechanical analysis (DMA), thermogravimetric analyses (TGA), Fourier-transform infrared spectroscopy (FTIR), 13 C cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy ( 13 C{ 1 H} CP-MAS NMR) and measures of proton spin-lattice relaxation time in the rotating frame ( T 1 ρ ( H )), in the laboratory frame ( T 1 ( H )) a…
Triterpenoid saponins from Piptadeniastrum africanum (Hook. f.) Brenan
2013
One new triterpenoid saponin, named piptadeniaoside (1), along with two known saponins (2–3) have been isolated from the stem bark of Piptadeniastrum africanum. After previous isolation of flavone derivatives from this plant, new phytochemical investigations were performed for its saponin content. Their structures were established by direct interpretation of their spectral data, mainly HRESIMS, 1D NMR (1H, 13C NMR, DEPT) and 2D NMR (COSY, NOESY, HSQC and HMBC), and by comparison with the literature data.
Characterization of some triphenyltin(IV) complexes of 5-(arylazo)salicylaldehyde ligands using IR, 1H, 13C, 119Sn NMR and 119Sn Mössbauer spectrosco…
1994
Abstract Coordination complexes of 5-(arylazo)salicylaldehyde with triphenyltin chloride have been prepared and subjected to IR, multinuclear NMR (1H, 13C, 119Sn) and 119Sn Mossbauer spectroscopy. 5-(Arylazo)salicylaldehyde forms two types of complexes viz. triorganotin adducts and phenoxides. In the adducts, the protonated ligand coordinates through the aldehydic oxygen atom while in phenoxides, the coordination occurs via the phenolic oxygen atom and the oxygen atom of the aldehydic group. The spectroscopic data suggest that both types of complexes adopt a cis-trigonal bipyramidal geometry around tin.