Search results for "MR"
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13C NMR spectra of eudesmanolides I—eudesman-12,6-olides
1987
The 13C NMR spectra of 26 eudesmanolides of natural and synthetic origin have been measured, including the naturally occurring sesquiterpene lactones artemisin, torrentin, rothin-A and rothin-B and several semi-synthetic eudesman-12,6-olides obtained from artemisin. The chemical shift values of the different compounds are compared and the effects of the substituents are discussed.
Complexation of enantiomerically pure tetraalkylammonium cations by ethyl resorcinarene
2013
Molecular recognition via weak interactions of three enantiopure tetraalkylammonium cations 2–4 by ethyl resorcinarene 1 was studied in the solid state using single-crystal X-ray diffraction, in solution by proton nuclear magnetic resonance spectroscopy (1H NMR) titration and in the gas phase using electrospray ionisation mass spectrometry. The 1H NMR titration studies reveal the association constants for the 1:1 complexes to vary according to the size and electronic properties of the alkyl groups of the guest cations. In the solid state, the resorcinarene is deprotonated and the X-ray structure confirms the 1:1 complex 2+@1− to be held together by multiple cation…π and C–H…π interactions.…
Effect of Heating Time and Temperature on the Chemical Characteristics of Biochar from Poultry Manure
2014
Poultry manure (PM) chars were obtained at different temperatures and charring times. Chemical-physical characterization of the different PM chars was conducted by cross-polarization magic angle spinning (CPMAS) (13)C NMR spectroscopy and thermal analysis. CPMAS (13)C NMR spectra showed that the chemical composition of PM char is dependent on production temperature rather than on production duration. Aromatic and alkyl domains in the PM chars obtained at the lowest temperatures remained unchanged at all heating times applied for their production. The PM char obtained at the highest temperature consisted only of aromatic structures having chemical nature that also appeared invariant with hea…
Dimethoxy aromatic compounds. IV.—determination of stereochemistry of 2,3,6,7-tetraalkoxy-9,10-dihalomethyl-9,10-dihydroanthracenes by13C NMR chemica…
1987
The analysis of the 13C NMR spectra of several 2,3,6,7-tetraalkoxy-9,10-dihalomethyl-9,10-dihydroanthracenes showed a strong dependence of the chemical shift values on the orientation of the halomethyl groups. On this basis it was possible to determine both the configuration (cis or trans) and conformation of the isomers, even if only one isomer was available.
The Synergetic Interplay of Weak Interactions in the Ion-Pair Recognition of Quaternary and Diquaternary Ammonium Salts by Halogenated Resorcinarenes
2013
The influence of halogens on the noncovalent interactions of different upper-rim-substituted hexylresorcinarenes with quaternary and diquaternary ammonium iodide salts was investigated in the gas phase by electrospray ionization Fourier-transform ion-cyclotron-resonance (ESI-FTICR) mass spectrometry and in solution by 1H NMR titration studies. The electronic nature of the substituents on the upper rim of the resorcinarene was directly reflected in the order of binding strengths of the hosts towards quaternary and diquaternary ammonium cations in the gas phase. In solution, the opposite trend was observed, with generally higher binding constants for the diquaternary over the quaternary salts…
Triple associates based on (oxime)Pt(II) species, 18-crown-6, and water: Synthesis, structural characterization, and DFT study
2014
Abstract The associates 2(cis-[PtCl2(acetoxime)2])⋅18-crown-6⋅2H2O (1), 2(cis-[PtBr2(acetoxime)2])⋅18-crown-6⋅2H2O (2), and trans-[PtCl2(acetaldoxime)2]⋅(18-crown-6)⋅2H2O (3) were synthesized by co-crystallization of free corresponding platinum species and 18-crown-6 from wet solvents and characterized by 1H NMR and IR spectroscopies, high-resolution mass-spectrometry (ESI), TG/DTA, and X-ray crystallography. The (oxime)Pt(II) species are assembled with 18-crown-6 and water by hydrogen bonding between the hydroxylic hydrogen atoms of the oxime ligands and the oxygen atom of water and between the hydrogen atoms of water and the oxygen atoms of 18-crown-6. In 2(cis-[PtX2(acetoxime)2])⋅18-crow…
Interactions between 2-Aminobenzothiazole and Natural Organic Matter as Evidenced by CPMAS Nitrogen-15 NMR Spectroscopy
2009
Cross-polarization magic angle spinning (CPMAS) 15N nuclear magnetic resonance (NMR) spectroscopy was used to study the interactions between 2-aminobenzothiazole (ABT) and natural organic matter in the presence of the natural enzyme laccase and synthetic air. Through the use of synthesized model compounds, we were able to confirm previous findings by CPMAS 13C NMR spectroscopy that showed the formation of covalent amide bonds. We also provide evidence of the presence of two additional H bonds between ABT and the natural organic matter. Both H bonds involved the amino and thiazole groups of ABT.
Recognition of N-Alkyl- and N-Aryl-Acetamides by N-Alkyl Ammonium Resorcinarene Chlorides
2014
N-alkyl ammonium resorcinarene chlorides are stabilized by an intricate array of intra- and intermolecular hydrogen bonds that leads to cavitand-like structures. Depending on the upper-rim substituents, self-inclusion was observed in solution and in the solid state. The self-inclusion can be disrupted at higher temperatures, whereas in the presence of small guests the self-included dimers spontaneously reorganize to 1:1 host-guest complexes. These host compounds show an interesting ability to bind a series of N-alkyl acetamide guests through intermolecular hydrogen bonds involving the carbonyl oxygen (C=O) atoms and the amide (NH) groups of the guests, the chloride anions (Cl(-)) and ammoni…
1H-nmr studies of polyoxyethylene-bound homo-oligo-L-methionines
1982
The use of 1H-nmr spectroscopy is demonstrated to be a useful analytical method to characterize the structure of synthetic peptides attached to soluble, macromolecular polyoxyethylene (POE) supports in the liquid-phase method (LPM) of peptide synthesis. We report an extensive 360-MHz 1H-nmr study of POE-bound homo-oligo-L-methionine peptides. A combination of high field and selective saturation or Redfield pulse methods allows resolution of individual backbone NH and α-CH resonances of dilute peptides in the presence of strong resonances from macromolecular POE and/or protonated solvents. The nmr spectra for the POE-bound peptides in CDCl3 are qualitatively similar to those of the low-molec…
Mononuclear mixed oxosulfidomolybdate(VI) complexes with aminodicarboxylic ligands. Synthesis and spectroscopic characterization by multinulcear magn…
1993
Addition of B2S3 to a methanolic solution of the MoVIO3L2− complex (L=N,N-bis(ethanoic acid)-1-amino-2- methylthio-ethane) results in the formation of two different monomeric oxosulfidomolybdate(VI) complexes, [MoO2SL]2− and [MoOS2L]2− as indicated by 1H, 13C, 17O and 95Mo NMR spectroscopy and by the reaction of these two sulfurated species with triphenylphosphine. The temperature dependences of the 1H NMR spectra indicate exchange processes for both sulfido complexes. Their redox properties are discussed and contrasted with those observed for the parent fac-trioxo molybdenum(VI) complex. The primary synthetic route to mixed oxosulfido [MoO3−nSnL]2− complexes described here can be extended …