Showing papers by "José Elguero published in 1977"
TL;DR: In this article, the 13C chemical shifts of 17 indazole derivatives are discussed as a function of substituent effects and the N-1-H or N-2-H structure of indazoles.
Abstract: The 13C chemical shifts of 17 indazole derivatives are discussed as a function of substituent effects and the N-1—H or N-2—H structure of indazole. The presence in solution of the N-1—H tautomer is confirmed.
29 citations
TL;DR: In this paper, the equilibrium constant in dioxane between azido and tetrazole isomers has been obtained for five heterocyclic azides (2-azido thiazoles, benzothiazole, benzoxazole, and 3 -azido isoxazoles) by prot...
Abstract: The equilibrium constant in dioxane between azido and tetrazole isomers has been obtained for five heterocyclic azides (2-azido thiazoles, benzothiazole, benzoxazole, and 3-azido isoxazole) by prot...
24 citations
TL;DR: In this article, the substituent effects on azido/tetrazole equilibrium on a series of 2-substituted thiazoles, benzothiazoles and isoxazoles have been studied by proton magnetic resonance in two solvents (DMSO-d6 and deuteriochloroform).
23 citations
TL;DR: The 1H, 13C, and 15N chemical shifts and coupling constants of 95%15N-enriched 1-phenyl-3-methylpyrazolin-5-one have been determined and assigned in this article.
Abstract: The 1H, 13C, and 15N chemical shifts and 1H–13C, 1H–15N, 13C–15N, and 15N–16N coupling constants of 95%15N-enriched 1-phenylpyrazole and 1-phenyl-3-methylpyrazolin-5-one have been determined and assigned. In the case of 3-methyl-1-phenyl [15N2]pyrazolin-5-one only the 15N n.m.r. spectrum [solvent (CD3)2SO] shows that slow exchange occurs between the NH and OH tautomers.
23 citations
TL;DR: In this article, the STO-3G ab initio SCF scheme was used to investigate the protonated species of the Z and E isomers of nitrous acid, with complete optimization of geometrical parameters.
18 citations
17 citations
16 citations
TL;DR: In this article, the value of the 3J(1HNN1H) coupling constant in hydrazides as a function of the dihedral angle was calculated using finite perturbation theory with INDO wave functions.
Abstract: Divers calculs, dont celui utilisant la methode des perturbations finies avec des fonctions d'onde INDO, ont ete effectues pour calculer la valeur du couplage 3J(1HNN1H) dans les hydrazides en fonction de l'angle diedre. Les resultats experimentaux (1H, 13C, 15N) sont examines a la lumiere de ces calculs. Le premier exemple d'un couplage 2J(1HN15N) est decrit.
Different calculations, among them those utilizing the finite perturbation theory with INDO wave functions, have been effected to calculate the value of the 3J(1HNN1H) coupling constant in hydrazides as a function of the dihedral angle. Experimental coupling constants have been compared with calculated ones in order to determine the conformation around the NN bond. The first example of a 2J(1HN15N) coupling is described.
15 citations
TL;DR: The 13C n.m. as discussed by the authors was used for the study of annular tautomerism in nine azapentalenes and very unusual couplings between the carbon atoms and the proton bonded to the pyrrole nitrogen atom were observed.
Abstract: L'etude en RMN du 13C de neuf azapentalenes a ete effectuee. Tous les signaux ont ete attribues. Dans un cas on a mis en evidence des couplages entre les atomes de carbone et l'hydrogene porte par l'azote pyrrolique, fait exceptionnel dans le cas des heterocycles aromatiques polyazotes. On demontre l'utilite de la RMN du 13C pour l'etude de la tautomerie annulaire.
The 13C n.m.r. study of nine azapentalenes was carried out and all the signals were assigned. In one case, very unusual couplings between the carbon atoms and the proton bonded to the pyrrole nitrogen atom were observed. The usefulness of 13C n.m.r. spectroscopy for the study of annular tautomerism is demonstrated.
13 citations
TL;DR: In this article, the signals of protons bonded to carbon atoms in α position to the pyridinic nitrogen atom in thiazole and in γ position to thiazolo[2,3-e]tetrazole are broadened.
Abstract: Les signaux des protons fixes sur un atome de carbone en α d'un azote pyridinique en serie thiazole et en γ en serie thiazolo[2,3-e]tetrazolique sont elargis a cause de la presence d'atomes d'azote 14N; cet elargissement disparait par irradiation, par refroidissement et en milieu acide (dans ce cas, cela permet la determination du site de protonation des deux molecules).
The signals of protons bonded to carbon atoms in α position to the pyridinic nitrogen atom in thiazole and in γ position in thiazolo[2,3-e]tetrazole are broadened. This broadening disappears on irradiation at the 14N resonance frequency, on cooling, and in an acidic medium (in which the protonation sites in both molecules can be determined).
5 citations
TL;DR: In this article, 1,3-diaryltriazenes in neutral and acidic solvents were studied using 1H-NMR and showed that at −80° the prototropic rate is slow enough to permit the observation of two aromatic systems.
Abstract: 1H-NMR. behaviour of 1,3-diaryltriazenes in neutral and acidic solvents
Formation and decomposition of 1,3-di-aryltriazenes can be studied by 1H-NMR. Triazenes decompose in acidic medium or by addition of isoamylnitrite: in the last case, the spectrum shows emission lines characteristic of the CINDP effect. At −80° the prototropic rate is slow enough to permit the observation of two aromatic systems.