Correlations between carbon-13 nuclear magnetic resonance and X-ray crystallography for pyrroles containing electron-withdrawing groups

1985 ◽  
Vol 63 (10) ◽  
pp. 2683-2690 ◽  
Author(s):  
J. B. Paine III ◽  
D. Dolphin ◽  
J. Trotter ◽  
T. J. Greenhough
Keyword(s):  
Chemical Shifts ◽  
Direct Methods ◽  
X Ray ◽  
Nmr Chemical Shifts ◽  
Competitive Effects ◽  
Bond Lengths ◽  
X Ray Crystallography ◽  
Phenyl Rings ◽  
Crystallographic Structures ◽  
C Nmr

The 13C nmr chemical shifts of benzyl 4-ethyl-3,5-dimethylpyrrole-2-carboxylate (1), methyl E-3-(3-ethyl-4,5-dimethylpyrrol-2-yl)-2-cyanopropenoate (2), and methyl E-3-(5-(benzyloxy)carbonyl-3-ethyl-4-methylpyrrol-2-yl)-2-cyanopropenoate (3) have been compared to their X-ray crystallographic structures. The 13C nmr chemical shifts were determined by direct comparison of a series of closely related homologs.Crystal data for 1, 2, and 3 are as follows: 1, monoclinic, P21/c, a = 14.934(2), b = 6.674(2), c = 15.269(2) Å, β = 101.96(1)°, Z = 4; 2, monoclinic, P21/n, a = 7.3030(3), b = 13.478(1), c = 12.985(1) Å, β = 97.48(1)°, Z = 4; 3, monoclinic, P21/c, a = 11.157(2), b = 13.109(2), c = 14.068(1) Å, β = 115.47(1)°, Z = 4. The structures were determined with diffractometer data by direct methods, and refined by full-matrix least-squares techniques to R = 0.052, 0.040, 0.038 for 862, 2032, 1483 reflexions, respectively. The molecules are approximately planar, except for deviations of the phenyl rings and of the terminal carbon atoms of the C3-ethyl groups from the molecular planes. The bond lengths in the pyrrole rings differ from those in pyrrole itself, as a result of the presence of the strongly electron-withdrawing sustituents; exocyclic bond lengths also exhibit differences from normal values.The competitive effects of the various electron withdrawing groups have been correlated to change in bond lengths, 13C chemical shifts, and the chemical reactions of the pyrrolic nucleus.

Selective chemistry of tripentaerythritol — Synthesis of acetals and their derivatives

2006 ◽  
Vol 84 (4) ◽  
pp. 516-521 ◽  
Author(s):  
Hussein Al-Mughaid ◽  
T Bruce Grindley
Keyword(s):  
Lewis Acid ◽  
Chemical Shifts ◽  
X Ray ◽  
Nmr Chemical Shifts ◽  
X Ray Crystallography ◽  
Catalysed Reaction ◽  
Toluenesulfonic Acid ◽  
C Nmr

Tripentaerythritol was converted efficiently into 2′,2′′:6′,6′′:10′,10′′-tri-O-cyclohexylidene-2,2,6,6,10,10-hexakis(hydroxymethyl)-4,8-dioxa-1,11-undecandiol (4) by the toluenesulfonic acid catalysed reaction with cyclohexanone in a mixture of N,N-dimethylformamide and benzene. Reaction of tripentaerythritol with benzaldehyde under similar conditions gave an easily separated mixture of the four possible stereoisomers. Structures of these stereoisomers were assigned based on 1H and 13C NMR chemical shifts using trends previously observed for the dibenzylidene acetals of dipentaerythritol, whose structures had been established unambiguously by X-ray crystallography. It was found that reduction of the mixture of benzylidene acetals to 2,6,10-tris(benzyloxymethyl)-4,8-dioxa-1,11-undecanediol could be accomplished using triethylsilane with ethylaluminium dichloride as the Lewis acid after a number of commonly used conditions for this transformation failed.Key words: pentaerythritol, tripentaerythritol, dipentaerythritol, acetals, benzylidene acetals, reduction.

Synthesis, X-ray structure determination, and formation of 3,4,5-trichloroguaiacol occurring in kraft pulp spent bleach liquors

1980 ◽  
Vol 58 (8) ◽  
pp. 815-822 ◽  
Author(s):  
K. Lindström ◽  
F. Österberg
Keyword(s):  
Reaction Mechanism ◽  
Melting Point ◽  
Structure Determination ◽  
Kraft Pulp ◽  
Chemical Shifts ◽  
X Ray ◽  
Nmr Chemical Shifts ◽  
Chemical Pulp ◽  
C Nmr

3,4,5-Trichloroguaiacol, which is formed during bleaching of chemical pulp and shown to bioaccumulate in fish, has been synthesized. The structure of the compound has been determined by means of X-ray analysis. The values of the 13C nmr chemical shifts and melting point differ from those previously reported. A reaction mechanism is suggested for the formation of 3,4,5- and 4,5,6-trichloroguaiacol.

Crystal and molecular structure of Z- and E-1,2-dichloro-1,2-bis(2-chlorophenyl)ethylene. An X-ray and NMR study

1995 ◽  
Vol 73 (9) ◽  
pp. 1520-1525
Author(s):  
Luciano Antolini ◽  
Ugo Folli ◽  
Dario Iarossi ◽  
Adele Mucci ◽  
Silvia Sbardellati ◽  
...  
Keyword(s):  
Chemical Shifts ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
X Ray ◽  
Nmr Study ◽  
Phenyl Rings ◽  
A Cell ◽  
C Nmr

The crystal structures of the title compounds were determined by single crystal X-ray diffraction techniques. The molecule of the Z isomer, which crystallizes in the monoclinic space group C2/c with Z = 4 in a cell of dimensions a = 14.891 (2), b = 10.780(2), c = 8.769(1) Å, β = 97.47(2)°, V = 1395.7(7) Å3 has crystallographic twofold symmetry. The E form crystallizes in the orthorhombic space group Pbca with a = 11.730(1), b = 6.932(1), c = 16.841(1) Å, V = 1369.4(2) Å3 and Z = 4. Its molecules have crystallographically dictated [Formula: see text] symmetry. In both isomers the phenyl rings are roughly perpendicular to the average ethylene plane. The atoms characterizing this plane show significant deviations from planarity in the Z isomer. Marked bond-angle distortions at the ethene carbons of both structures are observed. The 1H and 13C NMR spectra of the compounds were measured and, particularly in the case of the 1H chemical shifts, fall into two quite separate spectral regions. At low temperature, two conformational isomers, those with different relative orientation of the C—Cl bonds of the phenyl rings, are observed in the spectrum of each compound. Keywords: chlorostilbenes, overcrowded molecules. X-ray structure, conformations, NMR spectroscopy.

Halogenation of Tris(amido)tantalacarboranes with Dihalomethanes CH2X2 (X = Cl, Br)

2002 ◽  
Vol 67 (6) ◽  
pp. 791-807 ◽  
Author(s):  
Mark A. Fox ◽  
Andrés E. Goeta ◽  
Andrew K. Hughes ◽  
John M. Malget ◽  
Ken Wade
Keyword(s):  
Single Crystal ◽  
Prolonged Exposure ◽  
Chemical Shifts ◽  
Amide Group ◽  
The Other ◽  
X Ray ◽  
Nmr Chemical Shifts ◽  
X Ray Crystallography ◽  
H Nmr ◽  
Hydrolysis Of

Slow reactions of isomeric metallacarboranes of general formulae [(NMe2)3TaC2B9H11] (3 isomers) and [(NMe2)3TaC2B9H10Me] (3 isomers) with CD2Cl2 afford quantitative yields of monochloro complexes [Cl(NMe2)2TaC2B9H11] and [Cl(NMe2)2TaC2B9H10Me]. Exposure to CD2Cl2 for months leads to solutions containing about 70% of the dichlorides in three cases. More prolonged exposure of these and the other monochlorides leads to a mixture of boron-substituted complexes. Hydrolysis of [3,3,3-(NMe2)3-3,1,2-TaC2B9H11] by moist toluene results in the formation of the oxo-bridged complex 3,3'-[3,3-(NMe2)2-3,1,2-TaC2B9H11]2(μ-O), characterised by single-crystal X-ray crystallography. The limited solubility of the latter complex in CD2Cl2 eliminates the presence of this compound in the reaction of [3,3,3-(NMe2)3-3,1,2-TaC2B9H11] with CD2Cl2. The reaction of [2,2,2-(NMe2)3-2,1,12-TaC2B9H11] with CH2Br2 in C6D6 quantitatively yields the monobromide [2-Br-2,2-(NMe2)2-2,1,12-TaC2B9H11]. Prolonged reaction with CH2Br2 leads directly to isomeric boron-substituted complexes with no evidence for dibromides. The influence on 11B, 13C and 1H NMR chemical shifts of replacing an amide group in [(NMe2)3TaC2B9H11] with chloride to give [Cl(NMe2)2TaC2B9H11] is also discussed.

scholarly journals Informing NMR experiments with molecular dynamics simulations to characterize the dominant activated state of the KcsA ion channel

2020 ◽  
Author(s):  
Sergio Perez-Conesa ◽  
Eric G. Keeler ◽  
Dongyu Zhang ◽  
Lucie Delemotte ◽  
Ann E McDermott
Keyword(s):  
Molecular Dynamics ◽  
Chemical Shifts ◽  
Md Simulations ◽  
X Ray ◽  
Nmr Chemical Shifts ◽  
X Ray Crystallography ◽  
Activated State ◽  
State Present ◽  
Dynamics Simulations ◽  
Inference Techniques

As the first potassium channel with a X-ray structure determined, and given its homol- ogy to eukaryotic channels, the pH-gated prokaryotic channel KcsA has been extensively studied. Nevertheless, questions related in particular to the allosteric coupling between its gates remain open. The many currently available X-ray crystallography structures appear to correspond to various stages of activation and inactivation, offering insights into the molecular basis of these mechanisms. Since these studies have required mutations, com- plexation with antibodies, and substitution of detergents for lipids, examining the channel under more native conditions is desirable. Solid-state NMR (SSNMR) can be used to study the wild-type protein under activating conditions (low pH), at room temperature, and in bacteriomimetic liposomes. In this work, we sought to structurally assign the acti- vated state present in SSNMR experiments. We used a combination of molecular dynamics (MD) simulations, chemical shift prediction algorithms, and Bayesian inference techniques to determine which of the most plausible X-ray structures resolved to date best represents the activated state captured in SSNMR. We first identified specific nuclei with simulated NMR chemical shifts that differed significantly when comparing partially open vs. fully open ensembles from MD simulations. The simulated NMR chemical shifts for those spe- cific nuclei were then compared to experimental ones, revealing that the simulation of the partially open state was in good agreement with the SSNMR data. Nuclei that discrimi- nate effectively between partially and fully open states belong to residues spread over the sequence and provide a molecular level description of the conformational change.

Sterically Hindered Alkanes, II 1,1,1,3,3,3-Hexaphenylpropane

1982 ◽  
Vol 37 (12) ◽  
pp. 1623-1632 ◽  
Author(s):  
Werner Winter ◽  
Alfred Moosmayer ◽  
Anton Rieker
Keyword(s):  
Bond Angle ◽  
Direct Methods ◽  
Monoclinic Space Group ◽  
Crystal Modification ◽  
Mechanism Of Formation ◽  
Electron Transfer Mechanism ◽  
X Ray ◽  
Bond Lengths ◽  
Phenyl Rings ◽  
First Time

The structure of the title compound 3, C39H32, obtained for the first time by Schlenk and Bornhardt (1912) from triphenylmethyl (1) and diazomethane (2) has been determined by 14C-tracer technique, NMR spectroscopy and X-ray analysis. It crystallizes in the monoclinic space group C2/c with Z = 4, a = 9.943(6), b= 19.054(3), c = 14.708(2) Å and β = 101.80(2)°. The structure was solved by direct methods and refined by full-matrix least squares to R = 0.046 for all 2625 reflexions (|F0| >0). On account of steric repulsions between the phenyl rings at both termini the central propane bond angle φ is stretched to 127.2°, whereas the bond lengths are not much affected. The X-ray results are compared with those of Blount et al. (1982), obtained on a triclinic crystal modification (P1) of 3. A fair agreement of bond lengths and angles is observed, the slopes of the homochiral propellers, however, aro different in both modifications. The measurement of the N2- evolution shows that the mechanism of formation of 3 from 1 and 2 is different in the photochemical and dark reaction. A carbene respectively a one-electron transfer mechanism is suggested. In spite of the remarkably normal CC-propane bond lengths homolytic cleavage of these bonds to give 1 is observed at 200-220 °C using the ESR technique

Solid state and solution stereochemistry of crown ethers and models. ortho-Dimethoxydiphenyl ether and related dibenzo-15-crown-5 and tetrabenzo-30-crown-10 ethers as studied by X-ray crystallography and 1H and 13C NMR spectroscopy

1994 ◽  
Vol 72 (5) ◽  
pp. 1218-1224 ◽  
Author(s):  
G. W. Buchanan ◽  
A. Rodrigue ◽  
K. Bourque ◽  
A. C. Chiverton ◽  
I. R. Castleden ◽  
...  
Keyword(s):  
Solid Phase ◽  
Direct Methods ◽  
13C Nmr Spectroscopy ◽  
Structural Features ◽  
X Ray Diffraction ◽  
1H And 13C Nmr ◽  
Space Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
C Nmr

Solid phase 45.3 MHz 13C NMR spectra of ortho-dimethoxydiphenyl ether, 1, dibenzo[b,e]-15-crown-5- ether, 2, and tetrabenzo[b,e,q,t]-30-crown-10 ether, 3, have been obtained. Chemical shift trends are discussed in terms of the asymmetric units and structural features available from X-ray crystallographic data. Comparison with solution 13C spectra are made. The crystal structures of 1 and 3 were determined by X-ray diffraction at room temperature. 1 crystallizes in space group P21/a with a = 13.366(1), b = 8.230(1), c = 12.303(1) Å, β = 116.63(1)°, Z = 4. 3 crystallizes in space group P21/c with a = 7.903(1), b = 26.337(2), c = 7.852(1) Å, β = 97.28(1)°, Z = 2. The structures were solved by direct methods and refined by full-matrix least squares to residuals of 0.055 using 1727 reflections for 1 and of 0.042 using 2590 reflections for 3.

Crystal and solution structure of (E)-1,2-bis(ethylsulphonyl)cyclobutane-1,2-dicarbonitrile

1989 ◽  
Vol 54 (12) ◽  
pp. 3253-3259
Author(s):  
Jaroslav Podlaha ◽  
Miloš Buděšínský ◽  
Jana Podlahová ◽  
Jindřich Hašek
Keyword(s):  
Hydrogen Peroxide ◽  
Solution Structure ◽  
Peroxide Oxidation ◽  
X Ray ◽  
X Ray Crystallography ◽  
Nmr Study ◽  
Hydrogen Peroxide Oxidation ◽  
Unusual Product ◽  
C Nmr

The unusual product of the reaction of 2-chloroacrylonitrile with ethane thiol and following hydrogen peroxide oxidation was found to be (E)-1,2-bis(ethylsulphonyl)cyclobutane-1,2-dicarbonitrile by means of X-ray crystallography. 1H and 13C NMR study of this compound has proven the same conformation of the molecule in solution.

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