Results 121 to 130 of about 1,896 (172)

Determination of the Hammett σ-Constants for the Picryl Group

The Journal of Organic Chemistry, 1965
Abstract : By measuring the rates of reaction of meta and para-picrylbenzoic acids with diphenyldiazomethane in ethanol, the Hammett constants sigma sub meta and sigma sub para for the picryl group were found to be 0.433 and 0.413 respectively. The ordering and magnitude of these constants indicates that there is no resonance interaction of the picryl ...
Howard E. Ruskie, Lloyd A. Kaplan
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A theoretical treatment of Hammett's sigma constants

Recueil des Travaux Chimiques des Pays-Bas, 1953
AbstractA theoretical treatment is given of the connection between the structure and the position of a substituent S and the value of σs, from the Hammett equation: log ks/ko = ρ · σs. The theory is based on a wave mechanical calculation of the effect of S on the localisation energy of a reaction. The equations derived make it possible to calculate σs,
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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
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Hammett constants of some (Trialkylsilyl)alkyl groups

Bulletin of the Academy of Sciences of the USSR Division of Chemical Science, 1961
1. The results confirm that in various phenylsilanes silicon can occur in the Si−(V) state on account of free 3d orbitals. 2. The specific effect of a silicon atom on β-functional groups is clearly determined by the specific character of the structure of these compounds together with the induction effects of the silyl and functional ...
E. A. Chernyshev, N. G. Tolstikova
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Constant no more: reevaluating Hammett constants through spin-crossover

Inorganic Chemistry Frontiers
The spin-crossover phenomenon helped re-evaluate the existing Hammett constants that incorrectly classify electron-withdrawing and electron-donating groups to explain and predict magnetic behaviours, chemical reactivity and beyond.
Igor Nikovskiy, Dmitry Aleshin, Aleksei Anisimov, Valentin Novikov, Yulia Nelyubina   +4 more
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Hammett analysis of absolute carbene addition rate constants

Tetrahedron Letters, 1983
Abstract Absolute rate constants were determined for the additions of 5 5 -X-substituted ArCCl (X=CF 3 , Cl, H, CH 3 , CH 3 O) to tetramethylethylene, trimethylethylene, trans-pentene, and 1-hexene; good Hammett correlations were obtained with ϱ = +1.4 – 1.6.
R.A. Moss, L.A. Perez, N.J. Turro, I.R. Gould, N.P. Hacker   +4 more
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Hammett constants of the pyrroline-2, 5-dione ring

Chemistry of Heterocyclic Compounds, 1976
The electronic effect of the pyrroline-2,5-dione ring on the benzene ring in the case of N-aryl compounds is close to the effect exerted by halogens. The overall electron-acceptor effect depends markedly on the nature of the solvent. The electron-donor effect of conjugation is small.
V. D. Romanenko, N. N. Kalibabchuk, A. A. Rositskii, V. G. Zalesskaya, V. E. Didkovskii, S. V. Iksanova   +5 more
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Designing Acid Acid Co-Crystals−The Use of Hammett Substitution Constants

Crystal Growth & Design, 2009
Construction of defined supramolecular synthons is a key aim of crystal engineering. This work reports the use of Hammett substitution constants as a tool in the design of acid-acid cocrystals with a desired R2 2(8) hydrogen-bonded heterodimer. © 2009 American Chemical Society.
Chadwick, Keith, Sadiq, Ghazala, Davey, Roger J.; id_orcid 0000-0002-4690-1774, Seaton, Colin C., Pritchard, Robin G., Parkin, Andrew   +5 more
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Quantum chemical topology (QCT) descriptors as substitutes for appropriate Hammett constants

Organic & Biomolecular Chemistry, 2005
A technique called quantum topological molecular similarity (QTMS) was recently proposed [J. Chem. Inf. Comput. Sci., 2001, 41, 764] in order to construct a variety of medicinal, ecological and physical organic QSAR/QSPRs, based on modern ab initio wave functions of geometry optimised molecules, in combination with quantum chemical topology (QCT).
Smith, P. J., Popelier, P. L A; id_orcid 0000-0001-9053-1363   +1 more
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Linear 13C-H coupling constant-Hammett sigma-constant relations in substituted benzaldehydes

Journal of Chemical & Engineering Data, 1972
benzaldehydes, measuring the CI3 -H coupling constant of the aldehydic proton. As expected, the greater ability of the trigonal carbon atom to transmit the electronic effects of substituent X to this proton is reflected in the much greater sensitivity of the Cl3-H coupling constant to the electronic nature of X. Again excellent linear J-a relationships
Claude H. Yoder, Charles D. Schaeffer, Ronald E. Hess   +2 more
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