- المجال: Chemistry
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The International Union of Pure and Applied Chemistry (IUPAC) serves to advance the worldwide aspects of the chemical sciences and to contribute to the application of chemistry in the service of people and the environment. As a scientific, international, non-governmental and objective body, IUPAC ...
An excited dimer, "non-bonding" in the ground state. For example, a complex formed by the interaction of an excited molecular entity with a ground state counterpart of this entity.
Industry:Chemistry
An electronically excited complex of definite stoichiometry, "non-bonding" in the ground state. For example, a complex formed by the interaction of an excited molecular entity with a ground state counterpart of a different structure.
Industry:Chemistry
State of a system with energy higher than that of the ground state. This term is most commonly used to characterize a molecule in one of its electronically excited states, but can also refer to vibrational and/or rotational excitation in the electronic ground state.
Industry:Chemistry
This term applies in a general way to any multiparametric extension of the Hammett equation. It is sometimes used specifically for a form of dual substituent-parameter equation in which the actual value of the correlated property P under the influence of the substituent X is used, rather than the value relative to that for X = H. An intercept term h corresponding to the value of P for X = H is introduced, e.g.
<center>P = ασ<sub>I</sub> + βσ<sub>R</sub> + h</center>
The equation may be applied to systems for which the inclusion of further terms to represent other effects, e.g. steric, is appropriate.
Industry:Chemistry
A method in which ions are produced in a mass spectrometer from nonvolatile or thermally fragile organic molecules by bombarding the compound in the condensed phase with energy-rich neutral particles.
Industry:Chemistry
An experimentally observable effect symbolized by F (on reaction rates, etc.) of intramolecular coulombic interaction between the center of interest and a remote unipole or dipole, by direct action through space rather than through bonds. The magnitude of the field effect (or "direct effect") depends on the unipolar charge/dipole moment, orientation of dipole, shortest distance between the center of interest and the remote unipole or dipole, and on the effective dielectric constant. An approach to its calculation was described by Kirkwood and Westheimer (1938) and has been elaborated in more recent years.
Industry:Chemistry
Thermal reaction of a molecule by exposing it to a short thermal shock at high temperature, usually in the gas phase.
Industry:Chemistry
(1) The heterolytic cleavage of a molecule according to the general reaction
<center>a-b-c-d-X → (a-b)<sup>+</sup> + c=d + X<sup>-</sup></center>
where a-b is an electrofuge and X is a nucleofuge (which may emerge from the reaction in combined form), and the middle group affords the unsaturated fragment c=d. For example,
<center>Ph<sub>3</sub>C-CO<sub>2</sub>H + H<sup>+</sup> → Ph<sub>3</sub>C<sup>+</sup> + C=O + H<sub>2</sub>O</center>
GROB (1969).
(2) The breakdown of a radical into a diamagnetic molecule or ion and a smaller radical, e.g.,
<center>(CH<sub>3</sub>)<sub>3</sub>C-O<sup>.</sup> → (CH<sub>3</sub>)<sub>2</sub>C=O + H<sub>3</sub>C<sup>.</sup>
(ArBr)<sup>. -</sup> → Ar<sup>.</sup> + Br<sup>-</sup> (solution)</center>
(3) The breakdown of a radical ion in a mass spectrometer or in solution, forming an ion of lower molar mass and a radical, e.g.,
<center>((CH<sub>3</sub>)<sub>3</sub>C-OH)<sup>.+</sup> → (CH<sub>3</sub>)<sub>2</sub>C=OH<sup>+</sup> + H<sub>3</sub>C<sup>.</sup> (mass spectrometer)</center>
Industry:Chemistry
The Highest-energy Occupied Molecular Orbital (HOMO) (filled or partly filled) and Lowest-energy Unoccupied Molecular Orbital (LUMO) (completely or partly vacant) of a molecular entity. Examination of the mixing of frontier molecular orbitals of reacting molecular entities affords an approach to the interpretation of reaction behavior; this constitutes a simplified perturbation molecular orbital theory of chemical behavior.
Industry:Chemistry
Organic compounds are thought of as consisting of a relatively unreactive backbone, for example a chain of sp<sup>3</sup> hybridized carbon atoms, and one or several functional groups. The functional group is an atom, or a group of atoms that have similar chemical properties whenever it occurs in different compounds. It defines the characteristic physical and chemical properties of families of organic compounds.
Industry:Chemistry
