- Branche: 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 ...
Attractive forces between apolar molecules, due to their mutual polarizability. They are also components of the forces between polar molecules. Also called "dispersion forces".
Industry:Chemistry
Two paired electrons localized in the valence shell on a single atom. Lone pairs should be designated with two dots.
The term "nonbonding electron pair" is more appropriate, and is found in many modern text books.
Industry:Chemistry
The anion produced by hydron removal from a solvent molecule. For example, the hydroxide ion is the lyate ion of water.
Industry:Chemistry
The cation produced by hydronation of a solvent molecule. For example, CH<sub>3</sub>OH<sub>2</sub><sup>+</sup> is the lyonium ion of methanol.
Industry:Chemistry
Nuclei having the same resonance frequency in nuclear magnetic resonance spectroscopy and also identical spin-spin interactions with the nuclei of a neighboring group are magnetically equivalent. The spin-spin interaction between magnetically equivalent nuclei does not appear, and thus has no effect on the multiplicity of the respective NMR signals. Magnetically equivalent nuclei are necessarily also chemically equivalent, but the reverse is not necessarily true.
Industry:Chemistry
NMR method for determining kinetics of chemical exchange by perturbing the magnetization of nuclei in a particular site or sites and following the rate at which magnetic equilibrium is restored. The most common perturbations are saturation and inversion, and the corresponding techniques are often called "saturation transfer" and "selective inversion-recovery".
Industry:Chemistry
A general expression which correlates the Gibbs energy of activation (Δ<sup>†</sup>G) with the driving force (Δ<sub>r</sub>G<sup>o</sup>') of the reaction:
<center>Δ<sup>†</sup>G = (λ/4)(1 + Δ<sub>r</sub>G<sup>o</sup>'/λ)<sup>2</sup></center>
where λ is the reorganization energy and Δ<sub>r</sub>G<sup>o</sup>' is the standard free energy of the reaction corrected for the electrostatic work required to bring the reactants together. λ/4 is the intrinsic barrier of the reaction. Originally developed for outer-sphere electron transfer reactions, the Marcus equation has later been applied also to atom and group transfer reactions.
Industry:Chemistry
In the addition of hydrogen halides to unsymmetrically constituted (unsaturated) hydrocarbons, the halogen atom becomes attached to the carbon bearing the lesser number of hydrogen atoms. Originally formulated by Markownikoff (Markovnikov) to generalize the orientation in additions of hydrogen halides to simple alkenes, this rule has been extended to polar addition reactions as follows. " In the heterolytic addition of a polar molecule to an alkene or alkyne, the more electronegative (nucleophilic) atom (or part) of the polar molecule becomes attached to the carbon atom bearing the smaller number of hydrogen atoms."
This is an indirect statement of the common mechanistic observation, that the more electropositive (electrophilic) atom (or part) of the polar molecule becomes attached to the end of the multiple bond that would result in the more stable carbenium ion (whether or not a carbenium ion is actually formed as a reaction intermediate in the addition reaction). Addition in the opposite sense is commonly called "anti-Markovnikov addition".
Industry:Chemistry
At equilibrium, the product of the activities (or concentrations) of the reacting species is constant. Thus for the equilibrium
<center>αA + βB ⇌ γC + δD
K = (C)<sup>γ</sup>(D)<sup>δ</sup>/(A)<sup>α</sup>(B)<sup>β</sup></center>
Industry:Chemistry
A term which refers to the isolation of a reactive or unstable species by dilution in an inert matrix (argon, nitrogen, etc.), usually condensed on a window or in an optical cell at low temperature, to preserve its structure for identification by spectroscopic or other means.
Industry:Chemistry
