The Experts below are selected from a list of 264 Experts worldwide ranked by ideXlab platform
Rosa M Claramunt - One of the best experts on this subject based on the ideXlab platform.
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the structure of Azines derived from c formyl 1h imidazoles in solution and in the solid state tautomerism configurational and conformational studies
Magnetic Resonance in Chemistry, 2013Co-Authors: Joana Pinto, Vera L M Silva, Artur M S Silva, Rosa M Claramunt, Dionisia Sanz, Carmen M Torralba, Rosario M Torres, Felipe Reviriego, Ibon Alkorta, Jose ElgueroAbstract:The structures of three Azines derived from 2-formylimidazole, 4(5)-formylimidazole, and 4(5)-formyl-5(4)-methylimidazole have been determined in solution and in the solid state. Density Functional Theory (DFT) Polarizable Continuum Model (PCM) calculations (geometries, energies, and chemical shifts), NMR [solution and cross polarization magic-angle spinning (CPMAS)], and X-ray crystallography [azine of 4(5)-formylimidazole] have been used. The configuration around the central C = N bonds has been determined and some insights about prototropic tautomerism and conformation have been gained. Copyright © 2013 John Wiley & Sons, Ltd.
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the azido tetrazole and diazo 1 2 3 triazole tautomerism in six membered heteroaromatic rings and their relationships with aromaticity Azines and perimidine
Tetrahedron, 2010Co-Authors: Ibon Alkorta, Jose Elguero, Fernando Blanco, Rosa M ClaramuntAbstract:Abstract 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 points were used to discuss the ring-chain tautomerism of these compounds in relation with the aromaticity of the Azines (pyridine, pyrimidine, quinazoline, 1,3-diazapyrene, and perimidine) and the azoles (tetrazoles and 1,2,3-triazoles).
Christoforos G Kokotos - One of the best experts on this subject based on the ideXlab platform.
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2 2 2 trifluoroacetophenone as an organocatalyst for the oxidation of tertiary amines and Azines to n oxides
Chemistry: A European Journal, 2014Co-Authors: Dimitris Limnios, Christoforos G KokotosAbstract:A cheap, mild and environmentally friendly oxidation of tertiary amines and Azines to the corresponding N-oxides is reported by using polyfluoroalkyl ketones as efficient organocatalysts. 2,2,2-Trifluoroacetophenone was identified as the optimum catalyst for the oxidation of aliphatic tertiary amines and Azines. This oxidation is chemoselective and proceeds in high-to-quantitative yields utilizing 10 mol % of the catalyst and H2O2 as the oxidant.
Ibon Alkorta - One of the best experts on this subject based on the ideXlab platform.
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the structure of Azines derived from c formyl 1h imidazoles in solution and in the solid state tautomerism configurational and conformational studies
Magnetic Resonance in Chemistry, 2013Co-Authors: Joana Pinto, Vera L M Silva, Artur M S Silva, Rosa M Claramunt, Dionisia Sanz, Carmen M Torralba, Rosario M Torres, Felipe Reviriego, Ibon Alkorta, Jose ElgueroAbstract:The structures of three Azines derived from 2-formylimidazole, 4(5)-formylimidazole, and 4(5)-formyl-5(4)-methylimidazole have been determined in solution and in the solid state. Density Functional Theory (DFT) Polarizable Continuum Model (PCM) calculations (geometries, energies, and chemical shifts), NMR [solution and cross polarization magic-angle spinning (CPMAS)], and X-ray crystallography [azine of 4(5)-formylimidazole] have been used. The configuration around the central C = N bonds has been determined and some insights about prototropic tautomerism and conformation have been gained. Copyright © 2013 John Wiley & Sons, Ltd.
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the azido tetrazole and diazo 1 2 3 triazole tautomerism in six membered heteroaromatic rings and their relationships with aromaticity Azines and perimidine
Tetrahedron, 2010Co-Authors: Ibon Alkorta, Jose Elguero, Fernando Blanco, Rosa M ClaramuntAbstract:Abstract 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 points were used to discuss the ring-chain tautomerism of these compounds in relation with the aromaticity of the Azines (pyridine, pyrimidine, quinazoline, 1,3-diazapyrene, and perimidine) and the azoles (tetrazoles and 1,2,3-triazoles).
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barriers about double carbon nitrogen bond in imine derivatives aldimines oximes hydrazones Azines
Croatica Chemica Acta, 2009Co-Authors: Fernando Blanco, Ibon Alkorta, Jose ElgueroAbstract:The paper presents the results referring to the inversion mechanism of imines and their derivatives (hydrazones, oximes, Azines). The calculated barriers [B3LYP/6-311++G(d,p) and G3B3)] are in good agreement with the scarce existing data. The transition states correspond in all cases to a pure nitrogen inversion except in the case of Azines where they have some rotation character. The electron properties of the minima and the transition states have been characterized, allowing explanation of the geometrical changes observed in the process.
Rainer Glaser - One of the best experts on this subject based on the ideXlab platform.
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The azine bridge as a conjugation stopper: an NMR spectroscopic study of electron delocalization in acetophenone Azines.
Journal of Organic Chemistry, 2002Co-Authors: Michael Lewis, Rainer GlaserAbstract:Dipole parallel-alignment of organic molecular crystals of Azines has been achieved with a design that was based on the hypothesis that the azine bridge is a conjugation stopper. This hypothesis has now been tested in detail, and 1H and 13C NMR spectroscopic data of symmetric and unsymmetric acetophenone Azines are presented in support of this design concept. Previous structural, ab initio, and electrochemical studies have shown that the azine bridge largely inhibits through-conjugation in molecules with the general structure DPhC(Me)N−NC(Me)PhA, where D is a donor group and A is an acceptor group. NMR spectroscopy is an excellent tool to probe the degree of conjugation through the azine bridge. The NMR results reported here for nine symmetrical and 18 unsymmetrical Azines show in a compelling fashion that the hypothesis holds. Varying the donor group does not change the chemical shifts of the aromatic hydrogen and carbon atoms on the acceptor-substituted phenyl ring. Likewise, varying the acceptor group ...
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The crystal structure of 4-iodoacetophenone azine
Journal of Chemical Crystallography, 1999Co-Authors: Michael Lewis, Charles L. Barnes, Rainer GlaserAbstract:4-Iodoacetophenone azine crystallizes in the space group Pbcn with cell parametersa = 34.5187(19), b = 7.2638(4), and c = 6.3736(3) A. The azine shows a gauche conformation with regard to the N—N bond and the phenyl rings are twisted in a way that leads to the largest possible twist between the benzene rings of each azine. This azine conformation allows for intermolecular arene–arene T-contacts between pairs of benzene rings and these double-T contacts involve only molecules within the same layer. All Azines are perfectly colinear within each layer and this results in a quadrilateral kite-shaped arrangement of iodine atoms at the interface of each layer. The iodine-iodine distances within each layer are 4.5 and 5.1 A, and the three unique angles of the kite-shaped quadrilaterals are 97.1, 76.9, and 88.8°. The iodine atoms in adjacent layers pack such that atoms of one layer fill the square interstices of the next layer. The distances between iodine atoms in adjacent layers are 4.5 and 4.1 A. The C—I bonds are not orthogonal to the I-planes and the direction of the molecules in adjacent layers causes a deviation of about 40° from colinearity
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Push–pull substitution versus intrinsic or packing related N–N gauche preferences in Azines. Synthesis, crystal structures and packing of asymmetrical acetophenone Azines
Journal of The Chemical Society-perkin Transactions 1, 1995Co-Authors: Grace Shiahuy Chen, Charles L. Barnes, Jason K. Wilbur, Rainer GlaserAbstract:The asymmetrical E,E-configured para-disubstituted 4-methoxyacetophenone Azines with 4′-bromo-(1), 4′cyano-(2) and 4′-nitro-(3) substituents have been synthesized and their crystal structures have been determined. The synergetic reinforcement of ‘push’ and ‘pull’ effects does not suffice to overcome the intrinsic or packing induced N–N gauche preference, and Azines 1–3 all assume distinctly gauche N–N conformations (dihedral angle of 115–140°). The crystal packing is characterized by offset T-shaped and parallel displaced face-to-face arene-arene contacts between pairs of Azines with parallel or anti-parallel D→A orientations. This crystal architecture results in a net dipole of crystals of 1. The structural data are analysed in comparison with the symmetrical E,E-configured para-disubstituted acetophenone Azines 4–7. With regard to this best possible reference data set, the structural parameters of 1–3 do not show any significant manifestation of special electronic interactions over the N-perturbed extended π-system to be associated with the asymmetry of the Azines. While there exists no structural evidence of conjugation in these solid state structures, our results do not rule out asymmetry effects on the electronic structure of the ground or the excited states.
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Conjugation in Azines. Stereochemical analysis of benzoylformate Azines in the solid state, in solution, and in the gas phase
Journal of Organic Chemistry, 1993Co-Authors: Rainer Glaser, Grace Shiahuy Chen, Charles L. BarnesAbstract:The stereochemistry of benzoylformate Azines 3 was studied in the solid state (X-rays, IR), in solution ( 1 H-, 13 C-, and 15 N-NMR), and in the gas phase (ab initio theory). Benzoylformate Azines are excellent systems to study phenyl conjugation because the ester substituent is electron-withdrawing and in a conformation that impedes π backdonation thereby causing the azine-C to be highly electron-defficient and an excellent potential acceptor for π-donation. The X-ray structure of ethyl benzoylformate azine (3a) is reported and compared to the crystallographic record. Azines 3 assume the N-N s-trans conformation and the Z,Z configuration
Omer Zorba - One of the best experts on this subject based on the ideXlab platform.
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Significance of biogenic amines to food safety and human health
Food Research International, 1996Co-Authors: Ali R. Shalaby, Skru Kurt, Omer ZorbaAbstract:Biogenic amines are natural antinutrition factors and are important from a hygienic point of view as they have been implicated as the causative agents in a number of food poisoning episodes, and they are able to initiate various pharmacological reactions. Histamine, putrescine, cadaverine, tyramine, tryptamine, β-phenylethylamine, spermine, and spermidine are considered to be the most important biogenic amines occurring in foods. These amines are designated as biogenic because they are formed by the action of living organisms. Histamine has been implicated as the causative agent in several outbreaks of food poisoning, while tyramine and β-phenylethylamine have been proposed as the initiators of hypertensive crisis. The toxicity of biogenic amines to chicks in terms of loss of weight and mortality was also reported. The toxicity of histamine appeared to be enhanced by the presence of other amines such as cadaverine, putrescine, and tyramine. Biogenic amines may also be considered as carcinogens because of their ability to react with nitrites to form potentially carcinogenic nitrosamines. The biogenic amine content of various foods and feed have been widely studied and found in cheese, fish and meat products, eggs and mushrooms. Food substances that have been prepared by a fermentative process, or have been exposed to microbial contamination during aging or storage, are likely to contain amines. Alcoholic beverages such as beers can contain biogenic amines, as do some other fermented foods such as sauerkraut and soy bean products. Amines were also considered as endogenous to plant substance that is commonly used for food, where some fruits and vegetables were found to contain high concentrations of various amines.
