Results 221 to 230 of about 39,711 (263)
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Substituent effects on geminal proton–proton coupling constants
Canadian Journal of Chemistry, 1970The geminal coupling constants between the non-equivalent benzylic protons of a series of para- and meta-substituted N-benzyl-2-methylpiperidines were shown to be proportional to the Hammett σ constants of the substituents with ρ −1.38 in carbon tetrachloride, −1.21 in benzene, and nearly 0 in 1 N DCl solutions.
Y. L. Chow +3 more
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Conformational analysis of ribonucleosides from proton-proton coupling constants
Biochimica et Biophysica Acta (BBA) - Nucleic Acids and Protein Synthesis, 1980A graphical method is described which permits the determination in solution of conformational equilibria and parameters of ribonucleosides from proton-proton coupling constants. The method is based on the pseudorotational concept and the use of the Karplus equation.
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Determination of Proton Affinities and Acidity Constants of Sugars
The Journal of Physical Chemistry A, 2013Proton transfer reactions play a key role in the conversion of biomass derived sugars to chemicals. In this study, we employ high level ab initio theoretical methods, in tandem with solvation effects to calculate the proton affinities (PA) and acidity constants (pKa) of various d-glucose and d-fructose tautomers (protonation-deprotonation processes ...
Shuting, Feng +2 more
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The geminal tin—proton coupling constant: A comment
Journal of Organometallic Chemistry, 1977Abstract By consideration of typical examples and the general form of the contact contribution, it is shown that care must be exercised in basing conclusions on the geminal tin—proton coupling constant.
De Poorter, Bertha, Gielen, Marcel
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Talanta, 1975
The protonation constant of hexamethylenetetramine (urotropine) was determined by a potentiometric and a spectrophotometric method. The calculations gave log K(HL) (concentration constants): 4.89 at mu = 0.1 and 5.05 at mu = 0.5. The temperature was 25 degrees and potassium chloride was used to adjust the ionic strength.
A, Ivaska, L, Harju
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The protonation constant of hexamethylenetetramine (urotropine) was determined by a potentiometric and a spectrophotometric method. The calculations gave log K(HL) (concentration constants): 4.89 at mu = 0.1 and 5.05 at mu = 0.5. The temperature was 25 degrees and potassium chloride was used to adjust the ionic strength.
A, Ivaska, L, Harju
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A comparison of substituent effects on vicinal proton–proton and carbon–proton coupling constants
Canadian Journal of Chemistry, 1977Vicinal carbon–proton coupling constants have been determined for a series of tert-butyl derivatives and compared to the vicinal proton–proton coupling constants in the analogous series of isopropyl derivatives. In both series coupling constants were found to decrease with electronegativity of substituent, with 3JC,H decreasing more rapidly than 3JH,H.
T. P. Forrest, S. Sukumar
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Protonation constants of ?-alanine in electrolyte mixtures at constant ionic strength
Journal of Solution Chemistry, 1995The stoichiometric acid-base equilibrium constants for α-alanine in tetraethylamonium iodide-potassium nitrate solutions were determined at a constant ionic strength of 1.4 m at 25°C. The results obtained are discussed on the basis of the Friedman and the Pitzer model for electrolyte mixtures.
I. Brandariz +2 more
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Vicinal NMR Proton−Proton Coupling Constants. An NBO Analysis
The Journal of Physical Chemistry A, 2001A method of natural bond orbital (NBO) interactions between bonds and antibonds, σm → , has been developed for analyzing vicinal proton−proton coupling constants, 3JHH.
Angel L. Esteban +8 more
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The effect of substituents on geminal proton–proton coupling constants. III
Canadian Journal of Chemistry, 1977The effect of substituents at the 3-position in a series of N-methyl 5,6-dihydro-7H,12H-di-benzo[c,f]azocines on the geminal coupling constants of the C-12 methylene protons has been determined. The slope of the Hammett plot of 2J vs. σ has been found to be +0.20.
Roger N. Renaud +3 more
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Vicinal proton-proton coupling constants
Molecular Physics, 1989Ernesto Díez +4 more
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