(15N5)-Labeled Adenine Derivatives:  Synthesis and Studies of Tautomerism by15N NMR Spectroscopy and Theoretical Calculations

2001 ◽  
Vol 66 (16) ◽  
pp. 5463-5481 ◽  
Author(s):  
Avital Laxer ◽  
Dan T. Major ◽  
Hugo E. Gottlieb ◽  
Bilha Fischer
Keyword(s):  
Nmr Spectroscopy ◽  
Theoretical Calculations ◽  
Adenine Derivatives

Synthesis of 4-Aryl-3(5)-(2-hydroxyphenyl)pyrazoles by Reaction of Isoflavones and their 4-Thio Analogues with Hydrazine Derivatives

2007 ◽  
Vol 60 (12) ◽  
pp. 905 ◽  
Author(s):  
Albert Lévai ◽  
Artur M. S. Silva ◽  
José A. S. Cavaleiro ◽  
José Elguero ◽  
Ibon Alkorta ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Nmr Spectroscopy ◽  
Hydrogen Bonds ◽  
Hydrazine Hydrate ◽  
1H Nmr ◽  
Theoretical Calculations ◽  
Intramolecular Hydrogen Bonds ◽  
Nmr Study ◽  
Intramolecular Hydrogen ◽  
New Compounds

4-Aryl-3(5)-2-(hydroxyphenyl)pyrazoles have been prepared by the reaction of isoflavones and their 4-thio analogues with hydrazine hydrate and phenylhydrazine in hot pyridine. The reaction mechanism for the formation of these pyrazoles is discussed. All the new compounds have been fully characterized by NMR spectroscopy. In [D6]DMSO, a 1H NMR study allows observation of the presence of both pyrazole annular tautomers, due to the presence of intramolecular hydrogen bonds in each tautomer (OH···N and NH···O). Theoretical calculations have been carried out on tautomers and conformers of compounds 20 (3(5)-(2-hydroxy-4-methoxyphenyl)-5(3)-methyl-4-phenylpyrazole) and 21 (3(5)-(2-hydroxy-4-methoxyphenyl)-4-(2-methoxyphenyl)-5(3)-methylpyrazole), including the absolute shieldings (GIAO/B3 LYP/6–311++G**) of 21.

scholarly journals Silacyclohexanes, Sila(hetero)cyclohexanes and Related Compounds: Structure and Conformational Analysis

Molecules ◽  
2020 ◽  
Vol 25 (7) ◽  
pp. 1624 ◽  
Author(s):  
Bagrat A. Shainyan
Keyword(s):  
Nmr Spectroscopy ◽  
Electron Diffraction ◽  
Low Temperature ◽  
Conformational Analysis ◽  
Gas Phase ◽  
Theoretical Calculations ◽  
Gas Electron Diffraction ◽  
Experimental Measurements ◽  
Related Compounds

Conformational analysis of Si-mono- and Si,Si-disubstituted silacyclohexanes as well as their analogues with a heteroatom(s) in the ring is reviewed with the focus on the recent results. Experimental measurements in the gas phase (gas electron diffraction, GED) and low temperature NMR spectroscopy (LT NMR) on 1H, 13C and 29Si nuclei are described along with theoretical calculations at the DFT and MP2 levels of theory. Structural and conformational specific features are shown to be principally different from those of the carbon predecessors—the corresponding cyclohexanes, oxanes, thianes and piperidines. The role of various effects (steric, hyperconjugation, stereoelectronic, electrostatic) is demonstrated.

scholarly journals Hydrogenation Properties of LnAl2 (Ln = La, Eu, Yb), LaGa2, LaSi2 and the Crystal Structure of LaGa2H0.71(2)

Crystals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 193 ◽  
Author(s):  
Anton Werwein ◽  
Christopher Benndorf ◽  
Marko Bertmer ◽  
Alexandra Franz ◽  
Oliver Oeckler ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Hydrogen Gas ◽  
Hydrogen Atoms ◽  
Zintl Phases ◽  
Trigonal Bipyramidal ◽  
Transmission Electron ◽  
Hydrogenation Reactions ◽  
Lanthanide Metals

Many Zintl phases take up hydrogen and form hydrides. Hydrogen atoms occupy interstitial sites formed by alkali or alkaline earth metals and / or bind covalently to the polyanions. The latter is the case for polyanionic hydrides like SrTr2H2 (Tr = Al, Ga) with slightly puckered honeycomb-like polyanions decorated with hydrogen atoms. This study addresses the hydrogenation behavior of LnTr2, where the lanthanide metals Ln introduce one additional valence electron. Hydrogenation reactions were performed in autoclaves and followed by thermal analysis up to 5.0 MPa hydrogen gas pressure. Products were analyzed by powder X-ray and neutron diffraction, transmission electron microscopy, and NMR spectroscopy. Phases LnAl2 (Ln = La, Eu, Yb) decompose into binary hydrides and aluminium-rich intermetallics upon hydrogenation, while LaGa2 forms a ternary hydride LaGa2H0.71(2). Hydrogen atoms are statistically distributed over two kinds of trigonal-bipyramidal La3Ga2 interstitials with 67% and 4% occupancy, respectively. Ga-H distances (2.4992(2) Å) are considerably longer than in polyanionic hydrides and not indicative of covalent bonding. 2H solid-state NMR spectroscopy and theoretical calculations on Density Functional Theory (DFT) level confirm that LaGa2H0.7 is a typical interstitial metallic hydride.

Kinetics and Mechanism of the Formation of Ylides, 1, 4 or 1, 5-Diionic Organophosphorus and Phosphonate Esters: A Review

2018 ◽  
Vol 16 (1) ◽  
pp. 59-77 ◽  
Author(s):  
Sayyed Mostafa Habibi-Khorassani ◽  
Mehdi Shahraki ◽  
Bahareh Mostafa
Keyword(s):  
Nmr Spectroscopy ◽  
1H Nmr ◽  
1H Nmr Spectroscopy ◽  
Theoretical Calculations ◽  
Variable Temperature ◽  
Kinetics And Mechanism ◽  
Stopped Flow ◽  
Investigative Techniques ◽  
Phosphonate Esters

The kinetics and mechanism of the formation of some ylides,1,4 or 1,5-diionic organophosphorus and phosphonate esters have been reviewed. The UV-vis spectrophotometry, stopped-flow and variable-temperature 1H-NMR spectroscopy along with the theoretical calculations were used as investigative techniques.

Atropisomerism and conformational aspects of meso-tetraarylporphyrins and related compounds

2011 ◽  
Vol 15 (01) ◽  
pp. 1-28 ◽  
Author(s):  
Augusto C. Tomé ◽  
Artur M.S. Silva ◽  
Ibon Alkorta ◽  
José Elguero
Keyword(s):  
Nmr Spectroscopy ◽  
Theoretical Calculations ◽  
Comprehensive Description ◽  
Aryl Ring ◽  
X Ray ◽  
Conformationally Restricted ◽  
X Ray Crystallography ◽  
Picket Fence ◽  
Related Compounds

This review provides a comprehensive description of the atropisomerism of meso-di- and tetraarylporphyrins with substituents in ortho-positions of the aryl ring, as well as in corroles and in conveniently substituted phthalocyanines. Different methods of study were examined: X-ray crystallography, NMR spectroscopy (both static and dynamic aspects), classical kinetics, HPLC and theoretical calculations. Then the four atropisomers, the tautomerism of the inner protons, the 'picket fence' concept, conformationally restricted meso-tetraarylporphyrins and the influence of the metal on the conformation were discussed based on 250 references.

Structural characterization of dimeric indole alkaloids from Psychotria brachybotrya by NMR spectroscopy and theoretical calculations

2016 ◽  
Vol 57 (12) ◽  
pp. 1331-1334 ◽  
Author(s):  
Marcos A. dos S. Ribeiro ◽  
Carla M.B. Gomes ◽  
Anelise S.N. Formagio ◽  
Zefa V. Pereira ◽  
Ulisses Z. Melo ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Structural Characterization ◽  
Theoretical Calculations ◽  
Indole Alkaloids
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