- 行业: 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 ...
A set of empirical rules for certain formations of 3- to 7-membered rings. The predicted pathways are those in which the length and nature of the linking chain enables the terminal atoms to achieve the proper geometries for reaction. The disfavoured cases are subject to severe distortions of bond angles and bond distances.
Industry:Chemistry
A chemical species or molecular entity having an available pair of electrons capable of forming a covalent bond with a hydron (proton) or with the vacant orbital of some other species.
Industry:Chemistry
For Brønsted bases it means the tendency of a compound to act as hydron (proton) acceptor. The basicity of a chemical species is normally expressed by the acidity of the conjugate acid. For Lewis bases it relates to the association constants of Lewis adducts and π-adducts.
Industry:Chemistry
Shift of a spectral band to lower frequencies (longer wavelengths) owing to the influence of substitution or a change in environment. It is informally referred to as a red shift and is opposite to hypsochromic shift (blue shift).
Industry:Chemistry
The linear relation between energy of activation (E<sub>a</sub>) and enthalpy of reaction (ΔH<sub>r</sub>) sometimes observed within a series of closely related reactions.
<center>E<sub>a</sub> = A + BΔH<sub>r</sub></center>
Industry:Chemistry
1,2-Didehydrobenzene (the aryne derived from benzene) and its derivatives formed by substitution. The terms m- and p-benzyne are occasionally used for 1,3- and 1,4-didehydrobenzene, respectively.
Industry:Chemistry
Catalysis (usually for hydron transfer) by a bifunctional chemical species involving a mechanism in which both functional groups are implicated in the rate-controlling step, so that the corresponding catalytic coefficient is larger than that expected for catalysis by chemical species containing only one of these functional groups.
The term should not be used to describe the concerted action of two different catalysts ("concerted catalysis").
Industry:Chemistry
A specific region (or atom) in a molecular entity that is capable of entering into a stabilizing interaction with another molecular entity. An example of such an interaction is that of an active site in an enzyme with its substrate. Typical forms of interaction are by hydrogen bonding, coordination, and ion pair formation.
Two binding sites in different molecular entities are said to be complementary if their interaction is stabilizing.
Industry:Chemistry
There is a chemical bond between two atoms or groups of atoms in case that the forces acting between them are such as to lead to the formation of an aggregate with sufficient stability to make it convenient for the chemist to consider it as an independent "molecular species". In physical organic chemistry, this term refers usually to the covalent bond.
Industry:Chemistry
The average value of the gas-phase bond-dissociation energies (usually at a temperature of 298 K) for all bonds of the same type within the same chemical species. The mean bond energy for methane, for example, is one-fourth the enthalpy of reaction for
<center>CH<sub>4</sub>(g) → C(g) + 4H(g)</center>
Tabulated bond energies are generally values of bond energies averaged over a number of selected typical chemical species containing that type of bond.
Industry:Chemistry
