Enolates de β-cétoesters: conformations et stabilités des formes dissociées

1982 ◽  
Vol 60 (5) ◽  
pp. 634-642 ◽  
Author(s):  
C. Cambillau ◽  
F. Guibe
Keyword(s):  
Nmr Spectroscopy ◽  
A Priori ◽  
Experimental Results ◽  
Nmr Studies ◽  
H Nmr ◽  
Geometrical Constraints

The problem of the conformation of β-ketoester enolates has been investigated through 1H nmr studies and through conductimetrie studies. We have compared the dissociative properties of the K+ enolates of acyclic β-ketoesters which can a priori adopt any possible ZE, ZZ, EE, or EZ conformations and of hemicyclic β-ketoesters (2-carbethoxycyclopentanone, 2-acetyl γ-butyrolactone) in which geometrical constraints excluded some of them. The results lead to the conclusion that the EE conformation is more stable than either the ZZ or EZ ones. Confirmation of this point, which implies that the acyclic dissociated enolates exist in the EE conformation, is afforded by 1H nmr spectroscopy. Those experimental results have been complemented with abinitio STO-3G calculations performed on the methyl formylacetate anion and on the formylacetone anion (the diketonic analog). The method of conductimétrie titration by cryptand (2,2,2) used for the determination of the dissociation coefficient of K+ enolates in DMSO is discussed in some detail.

Determination of the content of fatty acid methyl esters (FAME) in biodiesel samples obtained by esterification using 1 H-NMR spectroscopy

2008 ◽  
Vol 46 (11) ◽  
pp. 1051-1054 ◽  
Author(s):  
Vinicius M. Mello ◽  
Flavia C. C. Oliveira ◽  
William G. Fraga ◽  
Claudia J. do Nascimento ◽  
Paulo A. Z. Suarez
Keyword(s):  
Fatty Acid ◽  
Nmr Spectroscopy ◽  
Fatty Acid Methyl Esters ◽  
Methyl Esters ◽  
H Nmr ◽  
Acid Methyl

Rhodium(I) complexes containing bidentate pyrazolylgallate ligands. X-ray crystal structures of [Me2Gapz2]Rh(COD), [Rh(μ-3,5-Me2pz)(CO)2]2, and [Rh(μ-3,5-Me2pz)(COD)]2

1984 ◽  
Vol 62 (6) ◽  
pp. 1057-1067 ◽  
Author(s):  
Brenda M. Louie ◽  
Steven J. Rettig ◽  
Alan Storr ◽  
James Trotter
Keyword(s):  
Solid State ◽  
Structural Parameters ◽  
Heavy Atom ◽  
Boat Conformation ◽  
Nmr Studies ◽  
Space Group ◽  
H Nmr ◽  
Square Planar ◽  
Dirhodium Complexes

The synthesis and characterization of the complexes [Me2Gapz2]Rh(LL) (where LL = COD, (CO)2, (PPh3)2, or (PPh3)(CO)), incorporating the bidentate, chelating, dimethylbis(1-pyrazolyl)gallate ligand are described. Non-rigidity in solution has been demonstrated by 1H nmr studies for some of the complexes. A crystal structure determination of the COD complex has confirmed the boat conformation for the Ga—(N—N)2—Rh six-membered ring in this complex in the solid state. In addition, the solid state structures of the 3,5-dimethylpyrazolyl bridged dirhodium complexes [Rh(μ-3,5-Me2pz)(CO)2]2 and [Rh(μ-3,5-Me2pz)(COD)]2 have been determined. Crystals of [Me2Gapz2]Rh(COD) are orthorhombic, a = 22.7447(8), b = 11.9776(5), c = 6.4635(3) Å, Z = 4, space group Pnma; those of [Rh(μ-3,5-Me2pz)(CO)2]2 are monoclinic, a = 8.7403(6), b = 16.3594(6), c = 25.434(2) Å, β = 95.286(3)°, Z = 8, space group P21/c; and those of [Rh(μ-3,5-Me2pz)(COD)]2 are triclinic, a = 10.350(2), b = 11.401(2), c = 12.355(2) Å, α = 112.485(7), β = 99.394(9), γ = 105.387(8)°, Z = 2, space group [Formula: see text]. All three structures were solved by conventional heavy atom techniques and were refined by full-matrix least-squares procedures to final conventional R values of 0.026, 0.024, and 0.037 for 1824, 5135, and 6109 reflections with I ≥ 3σ(I), respectively. In each case the Rh atoms have distorted square planar coordination geometry. Important mean structural parameters are Rh—N = 2.087(2), Rh—C = 2.129(2), [Formula: see text] for [Me2Gapz2]Rh(COD); Rh—N = 2.063(6), Rh—CO = 1.852(9), [Formula: see text] for [Rh(μ-3,5-Me2pz)(CO)2]2; and Rh—N = 2.084(1), Rh—C = 2.131(7), [Formula: see text] for [Rh(μ-3,5-Me2pz)(COD)]2.

Enantiomeric NMR discrimination of carboxylic acids using actinomycin D as a chiral solvating agent

2019 ◽  
Vol 17 (6) ◽  
pp. 1466-1470 ◽  
Author(s):  
Liwen Bai ◽  
Pian Chen ◽  
Jiangxia Xiang ◽  
Jiarui Sun ◽  
Xinxiang Lei
Keyword(s):  
Nmr Spectroscopy ◽  
Carboxylic Acids ◽  
Actinomycin D ◽  
H Nmr ◽  
Chiral Solvating Agent

We extended actinomycin D as a practical CSA for rapid enantiomeric determination of chiral carboxylic acids by1H NMR spectroscopy.

103Rh-NMR-Untersuchungen an Chloro-Bromo-Rhodaten(III) und Bestimmung der Stabilitätskonstanten im System [RhClnBr6-n]3-, n = 0-6 / 103Rh NMR Studies of Chloro-Bromo-Rhodates(III) and Determination of the Stability Constants in the System [RhCl„Br6-n]3-, n = 0-6

1989 ◽  
Vol 44 (11) ◽  
pp. 1402-1406 ◽  
Author(s):  
W. Kuhr ◽  
G. Peters ◽  
W. Preetz
Keyword(s):  
Nmr Spectroscopy ◽  
High Resolution ◽  
Stability Constant ◽  
Stability Constants ◽  
Trans Isomers ◽  
Nmr Studies ◽  
Downfield Shift ◽  
Overall Stability ◽  
The Stability

By 103Rh NMR spectroscopy the ten compounds of the system [RhCl„Br6_„]3-, n = 0-6 are identified by separate signals. A downfield shift of approximately 160 ppm is observed per substitution of Cl by Br, and the stereoisomers for n = 2, 3, 4 are separated by at least 4 ppm. From the relative intensities of the 103Rh signals in equilibrated solutions, whose total contents of Rh. Cl and Br are known, six individual stability constants are calculated. Their product gives the overall stability constant, indicating [RhBr6]3- to be 36,300 times more stable than [RhCl6]3-. On treatment of [RhBr6]3- with HCl cis/fac isomers are formed stereospecifically, whereas the reaction of [RhCl6]3- with HBr gives trans isomers, n = 2 and 4, containing 20—30% of the cis compounds; only mer-[RhCl3Br3] 3- is obtained pure. The high resolution spectra of [RhCl6]3- and [RhBr6]3- are exhibit five signals each, reflecting the intensity patterns of the most abundant isotopomers within [Rh35Cln37Cl6-n]3-, n = 2-6, and [Rh79Br„81Br6_„]3-, n = 1-5, respectively.

Chemical Shift Nonequivalence of Enantiomers of Amino Acid Derivatives in 1H NMR and 19F NMR Spectroscopy Induced by L-Chirasil- Val.

1992 ◽  
Vol 47 (7) ◽  
pp. 1034-1036 ◽  
Author(s):  
Bernhard Koppenhoefer ◽  
Michael Hummel
Keyword(s):  
Amino Acid ◽  
Nmr Spectroscopy ◽  
Chemical Shift ◽  
Methyl Esters ◽  
Enantiomeric Purity ◽  
Peak Splitting ◽  
H Nmr ◽  
Acid Methyl ◽  
Amino Acid Methyl Esters

Enantiomers of N-trifluoroacetyl-amino acid methyl esters in CC14 solution, after addition of the chiral polysiloxane (L)-Chirasil-Val, display a chemical shift nonequivalence ΔΔδ in both 1H NMR and 19F NMR spectroscopy. The effects found for the leucine and valine derivatives can be correlated with the thermodynamic parameters of interaction in the undiluted system, as determined by gas chromatography. In CDC13 solution, no peak splitting was observed. The method is potentially useful for the determination of the enantiomeric purity of substrates of low volatility.

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