A term to denote the tendency of a particular solvent to promote ionization of an uncharged or, less often, charged solute. The term has been used both in a kinetic and in a thermodynamic context. See also Dimroth-Reichardt ET parameter, Grunwald-Winstein equation, Z-value

A compound containing a large organic cation or anion which possesses a long unbranched hydrocarbon chain, e.g. H3C(CH2)nCO2-M+ H3C(CH2)nSO3-M+ H3C(CH2)nN(CH3)3+X- (n > 7). The existence of distinct polar (hydrophilic) and non polar (hydrophobic) regions in the molecule promotes the formation of micelles in dilute aqueous solution. amphiprotic ( [..]

The uncatalysed cleavage of one or more covalent bonds resulting from exposure of a compound to a raised temperature, or a process in which such cleavage is an essential part. See also pyrolysis

See Gibbs energy diagram, potential-energy profile

An activated complex, often characterized by the superscript , is defined as that assembly of atoms which corresponds to an arbitrary infinitesimally small region at or near the col (saddle point) of a potential energy surface. See also transition state

(IUPAC Recommendations 1994) B Continue from terms starting with A

A chemical species or molecular entity having an available pair of electrons capable of forming a covalent bond with a hydron (proton) (see Brønsted base) or with the vacant orbital of some other species (see Lewis base). See also hard base, superbase

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 (see conjugate acid-base pair). For Lewis bases it relates to the association constants of Lewis adducts and -adducts

See acidity function

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). IUPAC PHOTOCHEMICAL GLOSSARY (1992)