- 行业: Chemistry
- Number of terms: 1965
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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 ...
Stereoisomerism other than enantiomerism. Diastereoisomers (or diastereomers) are stereoisomers not related as mirror images. Diastereoisomers are characterized by differences in physical properties, and by some differences in chemical behavior toward achiral as well as chiral reagents.
Industry:Chemistry
A measure for the effect of a medium on the potential energy of interaction between two charges. It is measured by comparing the capacity of a capacitor with and without the sample present.
Industry:Chemistry
The transformation of a molecular entity A to give a molecular entity A<sub>2</sub>. For example:
<center>CH<sub>3</sub><sup>.</sup> + H<sub>3</sub>C<sup>.</sup> → CH<sub>3</sub>CH<sub>3</sub>
2 CH<sub>3</sub>COCH<sub>3</sub> → (CH<sub>3</sub>)<sub>2</sub>C(OH)CH<sub>2</sub>COCH<sub>3</sub>
2 RCOOH → (RCOOH)<sub>2</center></sub>
Industry:Chemistry
A solvent with a comparatively high relative permittivity (or dielectric constant), greater than ca. 15, and a sizable permanent dipole moment, that cannot donate suitably labile hydrogen atoms to form strong hydrogen bonds, e.g. dimethyl sulfoxide. The term (and its alternative "polar aprotic solvent") is a misnomer and is therefore discouraged. Such solvents are usually not aprotic, but protophilic (and at most weakly protogenic). In describing a solvent it is better to be explicit about its essential properties, e.g. dipolar and non-protogenic.
Industry:Chemistry
A bond formed (actually or conceptually) by coordination of two neutral moieties, the combination of which results in charge-separated structures, e.g.,
<center>R<sub>3</sub>N: + O → R<sub>3</sub>N<sup>+</sup>-O<sup>-</sup></center>
The term is preferred to the obsolescent synonyms "coordinate link", "co-ordinate covalence", "dative bond", "semipolar bond".
Industry:Chemistry
Intermolecular or intramolecular interaction between molecules or groups having a permanent electric dipole moment. The strength of the interaction depends on the distance and relative orientation of the dipoles. The term applies also to intramolecular interactions between bonds having permanent dipole moments.
Industry:Chemistry
Any chemical reaction of the type A + A → A' + A", where A, A' and A" are different chemical species. For example:
<center>2 ArH<sup>+</sup> → ArH + ArH<sup>2+</sup></center>
The reverse of disproportionation is called comproportionation.
A special case of disproportionation (or "dismutation") is "radical disproportionation", exemplified by
<center><sup>.</sup>CH<sub>2</sub>CH<sub>3</sub> + <sup>.</sup>CH<sub>2</sub>CH<sub>3</sub> → CH<sub>2</sub>=CH<sub>2</sub> + CH<sub>3</sub>CH<sub>3</sub></center>
Reactions of the more general type
<center>RC<sup>.</sup>HCH<sub>3</sub> + R'C<sup>.</sup>HCH<sub>3</sub> → RCH=CH<sub>2</sub> + R'CH<sub>2</sub>CH<sub>3</sub></center>
are also loosely described as radical disproportionations.
(A somewhat more restricted usage of the term prevails in inorganic chemistry.)
Industry:Chemistry
(1) The separation of a molecular entity into two or more molecular entities (or any similar separation within a polyatomic molecular entity). Examples include unimolecular heterolysis and homolysis, and the separation of the constituents of an ion pair into free ions.
(2) The separation of the constituents of any aggregate of molecular entities.
In both senses dissociation is the reverse of association.
Industry:Chemistry
A radical cation in which charge and radical sites are separated.
Industry:Chemistry
