The conformations of tartaric acids in aqueous solution studied by 1H and 13C nuclear magnetic resonance

1980 ◽  
Vol 58 (13) ◽  
pp. 1376-1379 ◽  
Author(s):  
José Ascenso ◽  
Victor M. S. Gil
Keyword(s):  
Aqueous Solution ◽  
Nuclear Magnetic Resonance ◽  
Tartaric Acid ◽  
High Dielectric Constant ◽  
Coupling Constants ◽  
Ph Values ◽  
Tartaric Acids ◽  
13C Nuclear Magnetic Resonance ◽  
Meso Form ◽  
High Dielectric

Vicinal H—H and C—H coupling constants are reported for (+)-tartaric acid and meso-tartaric acid at various pH values and used in a discussion of the conformation of these molecules. This is found not to change much with pH. For the meso form, in particular, the most favoured conformer is determined not so much by the possibility of internai [Formula: see text] hydrogen bonding but, at least in part, by stabilization of polar conformations in a sol vent (H2O) of high dielectric constant.

Complexes of tungsten(VI) with thiomalic acid studied by 1H and 13C nuclear magnetic resonance spectroscopy

1984 ◽  
Vol 62 (11) ◽  
pp. 2094-2100 ◽  
Author(s):  
M. Madalena Caldeira ◽  
Victor M. S. Gil
Keyword(s):  
Aqueous Solution ◽  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Sodium Tungstate ◽  
Stable Complex ◽  
Resonance Spectroscopy ◽  
Ph Values ◽  
13C Nuclear Magnetic Resonance ◽  
Metal Ligand

Proton and carbon-13 nmr evidence is presented on the number, stoichiometry, geometry, and stability of the complexes which form when sodium tungstate and (D,L)-thiomalic acid are mixed in aqueous solution at pH values in the range 2–7. In particular, three (or four) complexes are detected having a 1:2 composition (metal–ligand), as well as a less stable complex which seems to be a 1:1 species. Preliminary data are also given on the exchange of bound ligand in these complexes.

13C nuclear magnetic resonance study of cyclodipeptides containing 13C enriched hydrophobic amino acids

1980 ◽  
Vol 45 (2) ◽  
pp. 482-490 ◽  
Author(s):  
Jaroslav Vičar ◽  
François Piriou ◽  
Pierre Fromageot ◽  
Karel Bláha ◽  
Serge Fermandjian
Keyword(s):  
Amino Acids ◽  
Nuclear Magnetic Resonance ◽  
Nuclear Magnetic Resonance Study ◽  
Coupling Constants ◽  
Side Chain ◽  
Amino Acid Residues ◽  
Magnetic Resonance Study ◽  
Side Chain Conformation ◽  
13C Nuclear Magnetic Resonance ◽  
Hydrophobic Amino Acids

The diastereoisomeric pairs of cyclodipeptides cis- and trans-cyclo(Ala-Ala), cyclo(Ala-Phe), cyclo(Val-Val) and cyclo(Leu-Leu) containing 85% 13C enriched amino-acid residues were synthesized and their 13C-13C coupling constants were measured. The combination of 13C-13C and 1H-1H coupling constants enabled to estimate unequivocally the side chain conformation of the valine and leucine residues.

1H and 13C nuclear magnetic resonance studies of the conformational equilibrium of 2-(diphenylphosphino)benzaldehyde in polar and nonpolar solutions. Signs of the proximate coupling constants, 4J(CHO, 31P) and 3(13CHO, 31P)

1993 ◽  
Vol 71 (9) ◽  
pp. 1384-1393 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Robert W. Schurko ◽  
Frank E. Hruska
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Lone Pair ◽  
Pair Interaction ◽  
Coupling Constants ◽  
Torsion Angles ◽  
Solvent Dependence ◽  
13C Nuclear Magnetic Resonance ◽  
Repulsive Forces ◽  
Nuclear Magnetic

The analyses of the 1H nuclear magnetic resonance spectra of 2-(diphenylphosphino)benzaldehyde in CS2/C6D12 and acetone-d6 solutions yield stereospecific coupling constants from which the populations of the O-cis and O-trans conformers are derived. The free energy differences favouring the O-trans conformer at 300 K are 2.7 and 0.9 kJ/mol, in the polar and nonpolar solutions, respectively; in the crystal only the O-cis conformer exists. The coupling constant, 4J(CHO, P), is estimated as −7.1(2) Hz in the O-trans confomer and 3J(CHO, P) as +29.4(1.3) Hz. Their magnitudes depend on the proximity of the C—H bond to the lone pair on phosphorus. nJ(C, P) are reported for triphenylphosphine and for the benzaldehyde derivative as dilute solutions in the two solvents, demonstrating a significant solvent dependence for some of these coupling constants. Some simple relationships are proposed between nJ(C, P) and the torsion angle about the C—P bond, estimates of the latter coming from AM1 and STO 3G MO computations. nJ(C, P) are also sensitive to intrinsic ring substituent perturbations, as are the nJ(H, P); for example, 5J(H, P) is negative in the disubstituted ring of 2-(diphenylphosphino)benzaldehyde but positive in the phenyl groups. The nJ(H, P) are also discussed with respect to their dependence on the torsion angles about the C—P bonds. It appears that the conformational properties of the aromatic rings in triphenylphosphine and its formyl derivative are very similar. Further, the phosphorus atom is polarized such that the carbonyl bond is attracted towards the positive region near phosphorus, and the C—H bond of the formyl group more towards the lone-pair region; the actual torsion angles represent a compromise between these attractive forces and the repulsive forces between bonds on neighbouring aromatic moieties. CNDO/2 MO and INDO MO FPT computations of nJ(C, P) and nJ(H, P) are of mixed utility, although the former bear out the idea that the proximate [Formula: see text]lone-pair interaction dominates 3J(CHO,P) and 4J(CHO,P).

sHigh resolution 1H nuclear magnetic resonance studies of a flavine and its product with MoCl4

1977 ◽  
Vol 55 (4) ◽  
pp. 575-582 ◽  
Author(s):  
T. Roberie ◽  
N. S. Bhacca ◽  
J. Selbin
Keyword(s):  
Aqueous Solution ◽  
Nuclear Magnetic Resonance ◽  
Binding Sites ◽  
Nmr Spectra ◽  
Coupling Constants ◽  
Side Chain ◽  
Magnetic Resonance Studies ◽  
H Nmr ◽  
Metal Atoms ◽  
1H Nuclear Magnetic Resonance

The high resolution 1H nmr spectra of the substituted flavine, 3-N-methyltetraacetylriboflavine (3-Me-TARF), and its non-aqueous solution complexes with Gd(fod)3, Eu(fod)3, MoCl4, and MoCl4•2CH3(CH2)2CN, were studied in order to try to discern the binding sites of the flavine as it attaches to the molybdenum. Evidence was found that all three metal atoms, Gd(III), Eu(III), and Mo(IV), are attached in solution not only by the primary binding (chelating) sites of the flavine, viz., the O-4 and N-5 atoms, but also by an acetyl oxygen atom, at the C-4′ site of the ribityl side chain. 300 MHz spectra of the 3-Me-TARF have permitted the coupling constants for the side chain methine and methylene protons to be obtained.

Hydrolysis of Sesquimustards

2003 ◽  
Vol 56 (4) ◽  
pp. 309 ◽  
Author(s):  
Timothy D. St Quintin ◽  
D. Ralph Leslie ◽  
J. Grant Collins
Keyword(s):  
Aqueous Solution ◽  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Nuclear Magnetic Resonance Spectroscopy ◽  
Contaminated Soil ◽  
Resonance Spectroscopy ◽  
Sulfonium Ions ◽  
13C Nuclear Magnetic Resonance ◽  
Hydrolysis Of

The hydrolysis of the sesquimustards 1,2-bis(2-chloroethylthio)ethane (QN2) and 1,3-bis(2-chloroethylthio) propane (QN3) has been studied by 1H and 13C nuclear magnetic resonance spectroscopy. For both sesquimustards, stable cyclic sulfonium ions were observed in hydrolysis experiments in a 1 : 1 mixture of [D6]acetone and D2O. The cyclic sulfonium ions, which persist in the aqueous solution for up to a week, are likely to retain some toxicity and could possibly be used as markers for sesquimustards in the analysis of mustard-contaminated soil for chemical weapons treaty verification. The formation of a macrocyclic oxadithiaether was also demonstrated for QN2 but not QN3.

Sporidesmins. XV, The 13C nuclear magnetic resonance spectra of sporidesmin and sporidesmin-D. The evidence in the spectra for strain imposed by an epidithio bridge

1976 ◽  
Vol 29 (10) ◽  
pp. 2307 ◽  
Author(s):  
JW Ronaldson
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Coupling Constants ◽  
Carbonyl Groups ◽  
Proton Resonance ◽  
Methyl Proton ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
Electro Negativity ◽  
Magnetic Resonance Spectra

The proton-noise-decoupled 13C N.M.R. spectra of sporidesmin and sporidesmin-D are presented. The detailed assignments were worked out from the undecoupled spectrum of sporidesmin-D. The 3-methyl resonance moved downfield (by 7.3 ppm) upon cleavage of the -S-S- bridge in sporidesmin while the peaks of the two quaternary carbons to which the sulphurs are bound moved upfield (by 4.7 ppm). Lactam N-methyl and indoline N-methyl proton resonance decoupling showed that their p.m.r. assignments should be reversed. The electro-negativity of nitrogen, sulphur and carbonyl groups increased the coupling constants of the 3-CH3 by 7Hz and of the 11-CH by 10 Hz. The carbon of the lactam N-methyl was shielded by 14 ppm. There were six three-bond couplings, four HCN13C and two HCO13C, evident but no non-aromatic HCC13C couplings.

13C nuclear magnetic resonance spectra of 3,6-disubstituted pyridazines

1991 ◽  
Vol 69 (6) ◽  
pp. 972-977 ◽  
Author(s):  
Gottfried Heinisch ◽  
Wolfgang Holzer
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

The 13C nuclear magnetic resonance spectra of 17 3,6-disubstituted pyridazine derivatives have been systematically analyzed. Chemical shifts and various 13C, 1H coupling constants are reported. Attempts were made to correlate these data with results obtained from semiempirical molecular orbital calculations as well as with substituent electronegativities and Taft's substituent constants σI and σR0. Key words: 3,6-disubstituted pyridazines, 13C NMR spectroscopy, 13C, 1H spin coupling constants.

A 1H and 13C nuclear magnetic resonance study of nucleosides with methylated pyrimidine bases

1982 ◽  
Vol 60 (24) ◽  
pp. 3026-3032 ◽  
Author(s):  
Frank E. Hruska ◽  
Wayne J. P. Blonski
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Nuclear Magnetic Resonance Study ◽  
Coupling Constants ◽  
Magnetic Resonance Data ◽  
Proton Coupling ◽  
13C Nuclear Magnetic Resonance ◽  
Pyrimidine Bases ◽  
Nuclear Magnetic

Alkylated pyrimidine bases are of interest from the viewpoint of mutagenesis and carcinogenesis. 1H nuclear magnetic resonance data are presented for a series of ribosides and arabinosides alkylated at the O2,O4, N3, and C5 positions of the pyrimidine base. The data provide information about the stereochemical effects of base methylation. The J(5—6) proton coupling constants show that O-alkylation leads to a decrease in the π-bond order of the C5—C6 bond. The 13C chemical shifts are related to the tautomeric changes effected by O-alkylation.

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