NMR study of the protonation of domoic acid

1992 ◽  
Vol 70 (4) ◽  
pp. 1156-1161 ◽  
Author(s):  
John A. Walter ◽  
Donald M. Leek ◽  
Michael Falk
Keyword(s):  
Nmr Spectra ◽  
Domoic Acid ◽  
Spectral Parameters ◽  
Protonation Site ◽  
Nmr Study ◽  
C Nmr

The 1H and 13C NMR spectra of the amnesic shellfish poison, domoic acid, in H2O and D2O solutions have been studied as a function of pH or pD. The results yielded the NMR spectral parameters for each of the five protonation stages of domoic acid, provided accurate pKa values, and enabled each pKa to be associated with a particular protonation site.

13C and 119Sn NMR spectra of diphenyl- and dibenzyltin(IV) compounds and their complexes

1990 ◽  
Vol 55 (5) ◽  
pp. 1193-1207 ◽  
Author(s):  
Jaroslav Holeček ◽  
Antonín Lyčka ◽  
Karel Handlíř ◽  
Milan Nádvorník
Keyword(s):  
Internal Structure ◽  
Coordination Sphere ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spectral Parameters ◽  
The Real ◽  
119Sn Nmr ◽  
C Nmr

13C and 119Sn NMR spectra of diphenyl- and dibenzyltin(IV) compounds have been studied in solutions of coordinating and non-coordinating solvents. Regions of values of the δ(119Sn) chemical shifts have been determined which characterize individual types of coordination of the central tin atom. The values of 13C NMR spectral parameters, the δ(13C) chemical shifts and nJ(119Sn, 13C) coupling constants, have been used to describe the real shapes of coordination sphere of the central tin atom and to discuss the internal structure of the organic substituents and of the nature of their bonding linkage to the tin atom.

29Si, 13C and 31P NMR spectra of silicon-substituted ω-diphenylphosphinoalkyl silanes, (CH3)3-n(OC2H5)nSi(CH2)mP(C6H5)2

1982 ◽  
Vol 47 (3) ◽  
pp. 793-801 ◽  
Author(s):  
Jan Schraml ◽  
Martin Čapka ◽  
Harald Jancke
Keyword(s):  
Nmr Spectra ◽  
31P Nmr ◽  
Chemical Shifts ◽  
Additivity Rule ◽  
Ethoxy Group ◽  
Spectral Parameters ◽  
Nmr Spectrum ◽  
Nmr Parameters ◽  
13C And 31P Nmr ◽  
C Nmr

29Si, 13C, and 31P NMR spectra of a series of compounds of the structure (CH3)3-n(C2H5O)n.Si(CH2)mP(C6H5)2 (m = 1-6, n = )-3) are reported and assigned. Using monodeutero derivative of the compound with m = 3 and n = 0 an earlier assignment of 13C NMR spectrum is confirmed, but the assignment in the compounds with m = 4 is reversed. Introduction of ethoxy groups leads to violation of additivity rule for the 13C chemical shifts in the derivatives with m = 1. In all derivatives presence of one ethoxy group in the molecule has a profound effect on 31P chemical shift which is not changed by any further increase in the number of ethoxy groups in the molecule. The changes in 29Si chemical shifts follow the pattern known from other series of compounds. The observed trends in NMR parameters with changing n and m values can be explained by an interaction between phosphorus and oxygen atoms. Possible connections between the spectral parameters and catalysis employing the studied compounds are discussed.

Potentiometric and NMR study of ethylenediamine-N,N,N',N'-tetrakis[methylene(phenylphosphinic)] acid and its complexing properties

1989 ◽  
Vol 54 (3) ◽  
pp. 653-662 ◽  
Author(s):  
Ivan Lukeš ◽  
Petr Hermann ◽  
Pavel Pech
Keyword(s):  
Stability Constants ◽  
Nmr Spectra ◽  
Dissociation Constants ◽  
Phosphonic Acids ◽  
Nmr Study ◽  
Complexing Properties ◽  
C Nmr

The dissociation constants of ethylenediamine-tetrakis-[methylene(phenylphosphinic)] acid (H4edtmpPh) and its stability constants with Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Fe2+, Co2+ and Ni2+ have been determined. Study of the dependence of the 1H, 31P and 13C NMR spectra of H4edtmpPh solutions on the pH indicates that it is more similar to H4edta than to analogous phosphonic acids.

Synthesis and Variable Temperature 1H and 31P NMR Study of Phosphorus Ylides derived from reaction of NH-acids, triarylphosphine and acetylenic esters

2007 ◽  
Vol 2007 (6) ◽  
pp. 353-355 ◽  
Author(s):  
Seyyed Javad Sabounchei ◽  
Hassan Nemattalab
Keyword(s):  
Mass Spectroscopy ◽  
Nmr Spectra ◽  
31P Nmr ◽  
Variable Temperature ◽  
Phosphorus Ylides ◽  
Acetylenic Esters ◽  
Dialkyl Acetylenedicarboxylates ◽  
Nmr Study ◽  
One Step ◽  
C Nmr

A one-step synthesis of sterically congested phosphorus ylides in moderate to good yields by the reaction of dialkyl acetylenedicarboxylates, NH-acids and triarylphosphines are reported. Characterisation of the obtained compounds was performed by IR, 1H, 31P, 13C NMR, elemental analysis and mass spectroscopy. NMR spectra showed that some of these compounds (in CDCl3 as solvent) contained two rotamers with unequal populations that equilibrate rapidly at higher temperatures.

13C NMR study of 3-(X-benzal)phthalides and 2-(X-benzal)-1,3-indanediones

1980 ◽  
Vol 45 (10) ◽  
pp. 2772-2778 ◽  
Author(s):  
Eva Solčániová ◽  
Pavol Hrnčiar ◽  
Tibor Liptaj
Keyword(s):  
Chemical Shift ◽  
Nmr Spectra ◽  
Electronic Effect ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Carbonyl Groups ◽  
Aryl Group ◽  
Nmr Study ◽  
Derivatives Of ◽  
C Nmr

13C NMR spectra of 14 derivatives of 3-(X-benzal)phthalides (I) and 10 derivatives of 2-(X-benzal)-1,3-indanediones (II) were investigated. The correlation of 13C chemical shifts of carbon atoms of the phthalide ring with σ-constants showed that the electronic effect of substituents was transmitted from the benzylidene group of 3-(X-benzal)phthalides on the chemical shift of the carbonyl group not only through oxygen, but also through the aromatic ring of the phthalide moiety. The transmission of substituent effects in 2-(X-benzal)-1,3-indanediones on the chemical shift of the carbonyl groups was more pronounced on the carbonyl, which is in the trans-arrangement with respect to the aryl group. This phenomenon was also observed at carbon atoms of the benzene ring of the indanedione moiety closer to the trans-CO group.

X-Ray Structure Analysis and NMR Study of Sesquiterpene Lactone Hirsutolide

1995 ◽  
Vol 60 (2) ◽  
pp. 300-310 ◽  
Author(s):  
Urszula Rychłewska ◽  
Miloš Buděšínský ◽  
Halina Grabarczyk ◽  
Bohdan Drożdż ◽  
Miroslav Holub
Keyword(s):  
Crystal Structure ◽  
Nmr Spectra ◽  
Chair Conformation ◽  
Ring Conformation ◽  
X Ray ◽  
H Nmr ◽  
Nmr Study ◽  
Nmr Methods ◽  
The One ◽  
C Nmr

Hirsutolide, the C(8)-lactonized sesquiterpene of the heliangolide type has been studied by X-ray and NMR methods. In crystal the ten-membered ring conformation closely resembles the conformation observed in C(6)-lactonized heliangolides. This conformation, which can be described as a boat-chair is contrasted with the chair-chair conformation found in the crystals of other C(8)-lactonized heliangolide, scorpioidine. Broad signals in 1H and 13C NMR spectra indicated the conformation equilibrium in solution which was confirmed by observation of signals of two conformers (ca 3 : 1) in low temperature 1H NMR spectra. The major conformer is the one present in the crystal structure of hirsutolide and the minor conformer corresponds very likely to the one observed in the crystal structure of scorpioidine.

Sterically Crowded Heterocycles. I. Molecular Structure of 3-Chain Substituted 2-Phenylimidazo[1,2-a]pyridinium Salts

1994 ◽  
Vol 59 (12) ◽  
pp. 2677-2690 ◽  
Author(s):  
Stanislav Böhm ◽  
Richard Kubík ◽  
Martin Hradilek ◽  
Jan Němeček ◽  
Michal Hušák ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Nmr Spectra ◽  
Molecular Structures ◽  
Pyridinium Salts ◽  
Protonation Site ◽  
X Ray ◽  
H Nmr ◽  
C Nmr ◽  
Pyridinium Perchlorate

2-Phenyl-3-[(Z)-1,3-diphenyl-3-oxopropenyl]imidazo[1,2-a]pyridine (I) was converted to corresponding 1-alkyl-2-phenyl-3-[(Z)-1,3-diphenyl-3-oxopropenyl]imidazo[1,2-a]pyridinium salts III - VI and 2-phenyl- 3-[(Z)-1,3-diphenyl-3-oxopropenyl]imidazo[1,2-a]pyridinium perchlorate (VII). The protonation site is discussed in terms of calculated molecular energies of alternative cations. The X-ray structure analyses of enone I and its quaternary periodide III are reported and compared with the PM3 molecular optimizations. 1H NMR and 13C NMR spectra reveal well changes of molecular structures caused by the transformation of the base I into salts III - VII.

1H and 13C NMR study of (X-phenyl)-5-nitro-2-furylvinyl ethers

1980 ◽  
Vol 45 (12) ◽  
pp. 3557-3563 ◽  
Author(s):  
Miloslava Dandárová ◽  
Jaroslav Kováč ◽  
Daniel Végh
Keyword(s):  
Nmr Spectroscopy ◽  
13C Nmr ◽  
Nmr Spectra ◽  
Furan Ring ◽  
Chemical Shifts ◽  
1H And 13C Nmr ◽  
H Nmr ◽  
Nmr Study ◽  
Hammett Σ Constants ◽  
C Nmr

Reaction of 5-nitro-2-furylvinyltrimethylammonium bromide with substituted phenolates gave (E)- and (Z)-(X-phenyl)-5-nitro-2-furylvinyl ethers. The preffered s-cis and s-trans orientations of the furan ring in Z and E isomers, respectively, were determined by 1H NMR spectroscopy. To study the extent of p-π conjugation, 13C NMR spectra of compounds under investigation have also been measured and interpreted. Chemical shifts for ethylenic carbons and protons were correlated with Hammett σ constants.

Syntheses of model oligosaccharides of biological significance. XII. Synthesis, NMR, and conformational analysis of trideuteriomethyl 4-O-(β-D-mannopyranosyl)- 2-acetamido-2-deoxy-β-D-glucopyranoside: the use of DEPT 1H to 13C transfer for T1 measurements and NOE assignments of tightly coupled 1H nuclei

1992 ◽  
Vol 70 (10) ◽  
pp. 2607-2617 ◽  
Author(s):  
Ho Huat Lee ◽  
Ligaya N. Congson ◽  
Dennis M. Whitfield ◽  
Lajos R. Radics ◽  
Jiri J. Krepinsky
Keyword(s):  
Conformational Analysis ◽  
Molecular Conformation ◽  
Biological Significance ◽  
Semiempirical Method ◽  
Spin Lattice Relaxation ◽  
Proton Relaxation ◽  
Spectral Parameters ◽  
Rotational Angle ◽  
Nmr Study ◽  
C Nmr

The title disaccharide Manp(β1–4)GlcpNAcβ1-OCD3 has been prepared by a short synthetic sequence through the inversion of configuration from gluco to manno involving benzyl Glcp(β1–4)GlcpNAc. The disaccharide was subjected to detailed high-field 1H and 13C NMR study. First, conventional and 2D spectra were run to afford a complete set of assigned spectral parameters. Next, steady-state 1H–{1H} NOE and 1H, 13C spin lattice relaxation experiments were performed to infer dynamic spectral data related to molecular conformation. Owing to tight couplings and signal overlaps in the 1H spectrum, proton relaxation and selected NOE data were obtained via 13C NMR after transfer of the actual, non-equilibrium, proton magnetization to the 13C frequency domain. Using this experimental approach it has been found that T1's for Manp H-4 and GlcpNAc H-2 were substantially longer than those of the other sugar ring protons, and that the principal interresidue dipolar contact in Manp(β1-4)GlcpNAcβ1-OCD3 takes place between Manp H-1 and GlcpNAc H-4. Subsequently, a conformational analysis of the disaccharide was executed by means of a semiempirical method comparing Boltzman-averaged computed observables with experimental T1 and NOE values. The results suggest that the disaccharide has substantial conformational flexibility. Its exo-anomeric-stabilized conformational minimum at approximately [Formula: see text] of the glycosidic rotational angle is significantly populated but this global minimum does not represent the only rotational form available to the molecule.

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