author = "Claramunt, Rosa M."

Encontrado 233 documentos, página mostrada 1 de 24

NMR studies of novel Schiff bases derived from L-α-amino methyl esters and 3-hydroxypyridin-4-carboxaldehyde

Description: Schiff bases of 3-hydroxypyridin-4-carboxaldehyde and L-α-amino esters as well as those derived from the structurally related amines lacking the ester function have been synthesised. In two cases a tetrahydro-1H-imidazo[4,5- c]pyridine was formed as a by-product. 1H, 13C, 15N-NMR spectral data and d...
Language(s): Inglés

Oxalic acid/phenols and oxalic acid/cholesterol co-crystals: A solid state13C CPMAS NMR study

Description: The structures of the crystals obtained by mixing oxalic acid (1) and five hydroxy derivatives, phenol (2a), p-cresol (2b), hydroquinone (2c), β-naphthol (2d), and cholesterol (2e) have been studied by 13C CPMAS NMR. It has been proved that they are co-crystals of defined stoichiometry (oxalic/hydro...
Language(s): Inglés

Synthesis and spectroscopic properties of Schiff bases derived from 3-hydroxy-4-pyridinecarboxaldehyde

Description: A series of six new Schiff bases has been prepared by reacting aniline and 4-R-substituted anilines (R=CH3, OCH3, Br, Cl, NO 2) with 3-hydroxy-4-pyridinecarboxaldehyde. The 1H, 13C, 15N and 17O NMR data of these compounds are used to discuss the tautomerism. 15N NMR and 17O NMR chemical shifts estab...
Language(s): Inglés

A theoretical study of multinuclear coupling constants in pyrazoles

Description: The 243 coupling constants of eight N-R-pyrazoles [R = H, CH3, C6H5, COCH3, NH2, NO2, SO2CF3, Si(CH3)3] have been calculated and compared with 131 experimental values. The agreement is good and can be used to estimate new couplings. The whole collection has been statistically analyzed. Copyright © 2...
Language(s): Inglés

Solution and solid state (CPMAS) NMR studies of the tautomerism of six-membered heterocyclic compounds related to 2-pyridones

Description: Several 13C and 15N chemical shifts of 2-pyridone (1), 4(3H)-pyrimidone (2), uracil (3) and cytosine (4) have been measured in solution and in the solid state. These data have been discussed in relation with the tautomerism of the four heterocycles. GIAO ab initio calculations of absolute shieldings...
Language(s): Inglés

The use of chemical shifts vs. coupling constants for studying tautomerism: A combined experimental and theoretical approach

Description: When observing average NMR signals originated from a rapid equilibrium, the procedure to estimate the composition of the mixture is to use interpolation. To illustrate the difficulties of this approach, the much-studied case of the NH and OH tautomers of pyrazolinones will be reexamined. Calculated ...
Language(s): Inglés

Syntheses and structural studies of Schiff bases involving hydrogen bonds

Description: New Schiff bases have been prepared by reacting 3-hydroxy-4-pyridine- carboxaldehyde with various amines. NMR spectroscopic methods provided clear evidence that the Schiff bases exist in the solid state and in solution as hydroxyimino tautomers with the E-configuration. A study of the stabilities of...
Language(s): Inglés

13C and 15N NMR chemical shifts of 1-(2′,4′-dinitrophenyl) and 1-(2′,4′,6′- trinitrophenyl) pyrazoles in the solid state and in solution

Description: The 13C and 15N CPMAS NMR spectra of 18 pyrazoles substituted at position 1 by dinitrophenyl and trinitrophenyl (picryl) groups have been recorded. To help in the assignments, some of these compounds were studied in DMSO-d6 solution. Phenomena such as the conformation of the N-aryl groups and broade...
Language(s): Inglés

A molecular balance to measure the strength of N-H⋯π hydrogen bonds based on the tautomeric equilibria of C-benzylphenyl substituted NH-pyrazoles

Description: A theoretical (B3LYP/6-31G**) study of 30 pyrazoles, most of them existing in two tautomeric forms, has been carried out. 3(5)-(2-Benzylphenyl)-5(3)-methyl-1H-pyrazole (11) and 3(5)-(2-benzylbenzylphenyl)-5(3)-phenyl-1H-pyrazole (20) were synthesized from 2-benzoylacetophenone, and their annular tau...
Language(s): Inglés

The azido-tetrazole and diazo-1,2,3-triazole tautomerism in six-membered heteroaromatic rings and their relationships with aromaticity: Azines and perimidine

Description: The properties of 28 molecules together with 12 transition states belonging to the series of azido-azines, tetrazolo-azines, diazo-azines, and 1,2,3-triazolo-azines have been studied at the B3LYP/6-31G(d), B3LYP/6-311++G(d,p) and, for 26 cases, at the G3B3 level. Energies, NICS and bond critical poi...
Language(s): Inglés

Encontrado 233 documentos, página mostrada 1 de 24

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