- المجال: Chemistry
- Number of terms: 1965
- Number of blossaries: 0
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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 ...
A metal ion that combines preferentially with ligands containing ligating atoms that are the lightest of their Periodic Group.
Industry:Chemistry
A metal ion that combines preferentially with ligands containing ligating atoms other than the lightest of their Periodic Group.
Industry:Chemistry
The formation of a covalent bond by the combination or recombination of two radicals (the reverse of unimolecular homolysis). For example:
<center>HO<sup>.</sup> + H<sub>3</sub>C<sup>.</sup> → CH<sub>3</sub>OH</center>
Industry:Chemistry
In a considerable number of cases plots of T Δ<sup>†</sup>S vs. Δ<sup>†</sup>H, for a series of reactions, e.g. for a reaction in a range of different solvents, are straight lines of approximately unit slope. Therefore, the terms Δ<sup>†</sup>H and T Δ<sup>†</sup>S in the expression partially compensate, and Δ<sup>†</sup>G = Δ<sup>†</sup>H - T Δ<sup>†</sup>S often is a much simpler function of solvent (or other) variation than Δ<sup>†</sup>H or T Δ<sup>†</sup>S separately.
Industry:Chemistry
A molecular entity formed by loose association involving two or more component molecular entities (ionic or uncharged), or the corresponding chemical species. The bonding between the components is normally weaker than in a covalent bond.
The term has also been used with a variety of shades of meaning in different contexts: it is therefore best avoided when a more explicit alternative is applicable. In inorganic chemistry the term "coordination entity" is recommended instead of "complex".
Industry:Chemistry
A chemical reaction for which the expression for the rate of disappearance of a reactant (or rate of appearance of a product) involves rate constants of more than a single elementary reaction. Examples are "opposing reactions" (where rate constants of two opposed chemical reactions are involved), "parallel reactions" (for which the rate of disappearance of any reactant is governed by the rate constants relating to several simultaneous reactions to form different respective products from a single set of reactants), and stepwise reactions.
Industry:Chemistry
The reverse of disproportionation. The term "symproportionation" is also used.
Industry:Chemistry
Two or more primitive changes are said to be concerted (or to constitute a concerted process) if they occur within the same elementary reaction. Such changes will normally (though perhaps not inevitably) be "energetically coupled". (In the present context the term "energetically coupled" means that the simultaneous progress of the primitive changes involves a transition state of lower energy than that for their successive occurrence.) In a concerted process the primitive changes may be synchronous or asynchronous.
Industry:Chemistry
A (usually stepwise) reaction in which two or more reactants (or remote reactive sites within the same molecular entity) yield a single main product with accompanying formation of water or of some other small molecule, e.g. ammonia, ethanol, acetic acid, hydrogen sulfide.
The mechanism of many condensation reactions has been shown to comprise consecutive addition and elimination reactions, as in the base-catalyzed formation of (E)-but-2-enal (crotonaldehyde) from acetaldehyde, via 3-hydroxybutanal (aldol). The overall reaction in this example is known as the aldol condensation.
The term is sometimes also applied to cases where the formation of water or another simple molecule does not occur, as in "benzoin condensation".
Industry:Chemistry
The spatial arrangements of atoms affording distinction between stereoisomers which can be interconverted by rotation about formally single bonds. Some authorities extend the term to include inversion at trigonal bipyramidal centers and other "polytopal rearrangements".
Industry:Chemistry
