Results 221 to 230 of about 363,660 (280)

Computational Evaluation of σI and σR Substituent Constants

Journal of Molecular Structure, 2010
Abstract A computational approach for the evaluation of σ I and σ R substituent constants is outlined. It is based on correlations between theoretically evaluated electrostatic potential at nuclei (EPN) values for the carbon atoms ( V C ) in substituted benzene and bicyclo[2,2,2]octane derivatives containing the same polar group at position 1.
Sonia Ilieva, Boris Galabov, Diana Cheshmedzhieva   +2 more
exaly   +2 more sources

Substituent Correlations Characterized by Hammett Constants in the Spiropyran–Merocyanine Transition

The Journal of Physical Chemistry A, 2017
The modification of molecular properties by the use of substituents is a versatile route for molecular design. Here we show for the example of multiresponsive spiropyrans that substituent effects and their correlations can be accurately described by Hammett constants, which in turn can be obtained directly from density functional theory calculations ...
Oliver Brügner, Thomas Reichenbach, Michael Sommer, Michael Walter   +3 more
openaire   +4 more sources

Re-Examination of Steric Substituent Constants by Molecular Mechanics

International Journal of Molecular Sciences, 2005
: Statistical analysis employing the set of the steric constants Ωj,k(Rc) is shown to be very effective in characterizing the substituent steric effect on organic reactions. Ωj,k(Rc) contains several variable parameters which are useful for the diagnosis
Kazuhisa SAKAKIBARA, Minoru Hirota, Tomoaki Yuzuri   +2 more
exaly   +2 more sources

Substituent Constants of Azulene

Journal of Pharmaceutical Sciences, 1980
The ionization constants in water for six 3-substituted azuloic acids were determined spectrophotometrically. Conversion of these physical constants to their pKa values allowed a set of Hammett-type sigma values for the substituents on these acids to be calculated.
M R, Lichtenwalner, T J, Speaker
openaire   +2 more sources

Substituent constants for correlation analysis

Journal of Medicinal Chemistry, 1977
Constants for pi and omega ahve been measured for a miscellaneous group of aromatic substituents of interest to medicinal chemists. Swain and Lupton's gamma and kappa values have been calculated from the omego constants. Values for molar refractivity are also given for each of the substituents.
C, Hansch, S D, Rockwell, P Y, Jow, A, Leo, E E, Steller   +4 more
openaire   +2 more sources

The ?* constants of ionic substituents

Bulletin of the Academy of Sciences of the USSR Division of Chemical Science, 1976
1. We determined the chemical shifts in the31P NMR spectra of the compounds\((C_2 H_5 O)_2 P(O)SX (X = (CH_2 )_m \mathop S\limits^ + (CH_3 )C_2 H_5 \), (CH2)mSC2H5 (m=2–4 and 6)) and CnH2n+1 (n=6, 8), and obtained a linear correlation between δp and the σ* constants of the X substituents. 2.
Ya. L. Yarv, T. I. Pekhk, A. A. Aaviksaar, D. I. Lobanov, N. N. Godovikov   +4 more
openaire   +1 more source

Hammett Substituent Constants

2021
Benzoic acid ionizes into C6H5CO2− and H+ only partially in water. However, this ionization is rendered facile by electron-withdrawing substituents and more difficult by electron-rich substituents on the aromatic ring. The effect on ionization is also dependent on the position of the substituent on the ring in respect of the carboxylic acid group ...
openaire   +1 more source

An Efficient Computational Approach for the Evaluation of Substituent Constants

The Journal of Organic Chemistry, 2006
Density functional theory computations at the B3LYP/6-311+G(2d,2p) and BPW91/6-311G(d,p) levels were carried out for a series of 15 monosubstituted benzene derivatives to study dependencies between electronic structure parameters and experimental reactivity constants.
Boris, Galabov, Sonia, Ilieva, Henry F, Schaefer   +2 more
openaire   +2 more sources

Reestimation of the Taft's Substituent Constant of the Pentafluorophenyl Group

The Journal of Organic Chemistry, 2004
The Taft's substituent constant of the pentafluorophenyl group (sigma(C(6)F(5))) was reestimated to be 1.50 by correlation between IR spectral data (v(C)(=)(O)) and sigma constants for a series of esters (involving the pentafluorobenzyl group) of 3-phenylpropanoic acid and butanoic acid.
Toshinobu, Korenaga, Koichi, Kadowaki, Tadashi, Ema, Takashi, Sakai   +3 more
openaire   +2 more sources

Electrophilic Substituent Constant σ⁺ of Electron Donor Substituents in Nonpolar Media

The Journal of Organic Chemistry, 2009
The electrophilic substituent constant sigma(+) was derived from the relative rate constants of the solvolysis of substituted alpha-cumyl chlorides in an acetone/water solvent mixture in the original work by Brown and Okamoto (J. Am. Chem. Soc. 1958, 80, 4979).
Alexander, Oehlke, Alexander A, Auer, Katja, Schreiter, Katja, Hofmann, Franziska, Riedel, Stefan, Spange   +5 more
openaire   +2 more sources