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51.
Six β-diketones related to curcumin and curcumin itself have been studied by 13C NMR spectroscopy in chloroform in order to determine the equilibrium constant between the two keto/enol tautomers. In order to do this GIAO/B3LYP/6-31G∗∗ calculations of absolute shieldings (σ, ppm) were carried out. To establish relationships between σ and experimental chemical shifts (δ, ppm), three simple β-diketones (acetylacetone, dibenzoylmethane and benzoylacetone) have been studied. The preference for different groups to be conjugated with the CO has been determined. 相似文献
52.
The (13)C and (15)N 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-d(6) solution. Phenomena such as the conformation of the N-aryl groups and broadening of splittings due to quadrupolar nuclei are discussed. 相似文献
53.
Maria das Dores M.C. Ribeiro da Silva Manuel A.V. Ribeiro da Silva Vera L.S. Freitas Maria Victoria Roux Pilar Jimnez Juan Z. Dvalos Pilar Cabildo Rosa M. Claramunt Jos Elguero 《The Journal of chemical thermodynamics》2008,40(9):1378-1385
Thermophysical and thermochemical studies have been carried out for crystalline parabanic acid. The thermophysical study was made by differential scanning calorimetry, DSC, over the temperature interval between T = (263 and 473) K. Two phase transitions were found: at T = (392.3 ± 1.6) K with the enthalpy of transition of (2.1 ± 0.4) kJ · mol−1 and at T = (509.8 ± 1.5) K, when the compound was scanned to its fusion temperature. The standard (p = 0.1 MPa) molar enthalpy of formation, at T = 298.15 K, for crystalline parabanic acid was determined using static-bomb combustion calorimetry as −(590.2 ± 1.0) kJ · mol−1. The standard molar enthalpy of sublimation, at T = 298.15 K, was derived from the variation of their vapour pressures, measured by the Knudsen-effusion method, with the temperature. These two thermochemical parameters yielded the standard molar enthalpy of formation in the gaseous phase, at T = 298.15 K, as −(470.8 ± 1.2) kJ · mol−1. 相似文献
54.
1H-, 13C-, and 15N-NMR studies of five nitrobenzene-1,2-diamines in solution and solid state have been achieved and the experimental chemical shifts and coupling constants agree with the theoretical values obtained at the B3LYP/6-311 + +G(dp) computational level using the geometries fully optimized with the hybrid HF/DFT B3LYP method and the 6-31G(d) basis set. The GIAO approximation has been used to calculate the absolute shieldings. The contribution of the substituents to the 15N chemical shifts of the amino groups could be quantified using a presence/absence matrix and a multiple regression. 相似文献
55.
Rosa M. Claramunt Dionisia Sanz Concepción López Elena Pinilla M. Rosario Torres José Elguero Pierre Nioche C. S. Raman 《Helvetica chimica acta》2009,92(10):1952-1962
The existence of polymorphism in parent indazolin‐3‐one (=1,2‐dihydro‐3H‐indazol‐3‐one; 1 ) is reported as well as an X‐ray and NMR CPMAS study establishing that its 7‐nitro derivative 2 exists as the 3‐hydroxy tautomer. Absolute shieldings calculated at the GIAO/B3LYP/6‐311++G(d,p) level were used to determine the tautomeric oxo/hydroxy equilibrium in solution, i.e., always the 1H‐indazol‐3‐ol tautomer predominates. 相似文献
56.
Martyn P. Coles Majid S. Khalaf Rosa M. Claramunt M. Angeles García Ibon Alkorta José Elguero 《Journal of Physical Organic Chemistry》2010,23(6):526-535
In this paper, we report an example of intermolecular solid‐state proton transfer in the bicyclic guanidine, hppH. A combination of X‐ray crystallography, CPMAS NMR (13C and 15N) and theoretical calculations allows us to determine that a double proton transfer takes place in the (hppH)2 dimer with an activation energy of about 50 kJ mol?1. According to the B3LYP/6‐311++G(d,p) calculations, the double proton transfer occurs non‐symmetrically through a zwitterion. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
57.
Guy J. Clarkson M. ngeles Farrn Rosa M. Claramunt Ibon Alkorta Jos Elguero 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(3):271-276
The molecular structure of the anti‐aging agent J147 [systematic name: (E)‐N‐(2,4‐dimethylphenyl)‐2,2,2‐trifluoro‐N′‐(3‐methoxybenzylidene)acetohydrazide], C18H17F3N2O2, has been determined at 150 K. The crystal structure corresponds to the minimum‐energy conformation in the gas phase calculated by density functional theory (DFT). 15 other conformations have been calculated and compared with the minimum, denoted 1111 . NMR spectroscopic data have been obtained and compared with those from Gauge Independent Atomic Orbital (GIAO) calculations. DFT calculations allow the reduction of the 16 possible rotamers to the four most stable (i.e. 1111 , 1112 , 1121 and 1222 ); in addition, the calculated barriers connecting these minima are low enough to permit their interconversion. Comparison of the NMR spectroscopic results, both experimental and calculated, point to the 1121 isomer being present in chloroform solution. 相似文献
58.
Holzer W Claramunt RM López C Alkorta I Elguero J 《Solid state nuclear magnetic resonance》2008,34(1-2):68-76
A solid-state NMR/theoretical study of the tautomerism of 4-substituted pyrazolinones was carried out in search of new desmotropes. Thus, the systematic exploration by (13)C and (15)N CPMAS NMR of a series of 4-acylpyrazolin-5-ones has allowed to determine their structure in the solid state and to find a new example of desmotropy that of 1-phenyl-4-acetyl-pyrazolinone. 相似文献
59.
60.