Results 211 to 220 of about 18,999 (260)
Some of the next articles are maybe not open access.
Predicting Protonation Constants in Polyazaalkanes
Journal of Chemical Research, 1998An easy model which allows to calculate protonation constants in polyamines containing n equivalent or near equivalent protonation sites from simple molecular analysis is reported.
José Manuel Lloris +3 more
openaire +1 more source
Protonation rate constants of proline
Journal of Molecular Liquids, 1984Abstract The rate constants for protonation reactions of proline positive ion and zwitterion have been measured using a modulated temperature chemical relaxation method. The results are contrasted with those obtained for amino acids.
M.A. Slifkin, S.M. Ali
openaire +1 more source
The effect of substituents on geminal proton–proton coupling constants
Canadian Journal of Chemistry, 1967A series of 2-benzyloxytetrahydropyrans bearing substituents at the ortho, meta, and para positions of the benzene ring have been synthesized. From the nuclear magnetic resonance spectrum of each compound, the geminal coupling constant (J) between the non-equivalent protons of the benzylic methylene group was determined.
Robert R. Fraser +2 more
openaire +1 more source
Proton‐proton coupling constants in the unsubstituted pyrylium cation
Organic Magnetic Resonance, 1973AbstractAn iterative analysis of the PMR spectrum of the title compound was performed and the calculated values of spectral parameters, relative chemical shifts, proton‐proton and direct carbon‐proton couplings are compared with those of pyridine.
L. Radics, Julia Kardos
openaire +1 more source
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
openaire +1 more source
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.
openaire +2 more sources
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
openaire +2 more sources
Spectrophotometric determination of the first protonation constant of orthovanadate
Talanta, 1990The first protonation constant for VO(3-)(4) has been determined spectrophotometrically at 25 degrees in 1M sodium chloride and found to have the value log K = 13.29 +/- 0.01. Individual absorption spectra for VO(3-)(4) and HVO(2-)(4) have been calculated (for the range 218-350 nm) from experimental absorbance measurements.
J J, Cruywagen, J B, Heyns
openaire +2 more sources
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
openaire +2 more sources
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
openaire +2 more sources
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
openaire +2 more sources