- المجال: 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 ...
An isotope effect due to isotopes other than those of hydrogen.
Industry:Chemistry
An equation of the form
<center>pH = pK<sub>a</sub> - lg((HA)/(A<sup>-</sup>))</center>
for the calculation of the pH of solutions where the ratio (HA)/(A<sup>-</sup>) is known.
Industry:Chemistry
(1) Association between a base and the conjugate acid of a different base through a hydrogen bond (B'<sup>....</sup>HB<sup>+</sup> or A'H <sup>....</sup>A<sup>-</sup>). The term has its origin in the conjugate acid-base pair and is in no way related to conjugation of orbitals. Heteroassociation is a more appropriate term.
(2) Some authors refer to conjugated systems containing a heteroatom, e.g. pyridine, as "heteroconjugated systems". This usage is discouraged since it inappropriately suggests an analogy to homoconjugation (2), and conflicts with the currently accepted definition of that term.
Industry:Chemistry
Transition metal or Main Group compounds having more than one type of ligand.
Industry:Chemistry
The energy required to break a given bond of some specific compound by heterolysis. For the dissociation of a neutral molecule AB in the gas phase into A<sup>+</sup> and B<sup>-</sup> the heterolytic bond-dissociation energy D(A<sup>+</sup>B<sup>-</sup>) is the sum of the bond dissociation energy, D(A-B), and the adiabatic ionization energy of the radical A<sup>.</sup> minus the electron affinity of the radical B<sup>.</sup>.
Industry:Chemistry
A parameter measuring the cohesion of a solvent (energy required to create a cavity in the solvent).
Industry:Chemistry
The principal alkene formed in the decomposition of quaternary ammonium hydroxides that contain different primary alkyl groups is always ethylene, if an ethyl group is present. Originally given in this limited form by A.W. Hofmann, the rule has since been extended and modified as follows: "When two or more alkenes can be produced in a β-elimination reaction, the alkene having the smallest number of alkyl groups attached to the double bond carbon atoms will be the predominant product." This orientation described by the Hofmann rule is observed in elimination reactions of quaternary ammonium salts and tertiary sulfonium salts, and in certain other cases.
Industry:Chemistry
(1) An acronym for Highest Occupied Molecular Orbital. See frontier orbitals.
(2) A prefix (consisting of lower case letters, homo,) used to indicate a higher homologue of a compound.
Industry:Chemistry
(1) Association between a base and its conjugate acid through a hydrogen bond (B<sup>...</sup>HB<sup>+</sup> or AH<sup>...</sup>A<sup>-</sup>). Homoassociation is a more appropriate term for this phenomenon.
(2) The orbital overlap of two pi systems separated by a non-conjugating group, such as CH<sub>2</sub>.
Industry:Chemistry
