Encyclopedia of Chemistry

accurate from 4.3 billion years (the age of the Earth) to about 100,000 years before the present. Radiocarbon Dating SeeRADIOCAR ...

A rate-controlling step defined in the way recom- mended here has the advantage that it is directly related to the interpretatio ...

the “rate of conversion” and is appropriate when the use of concentrations is inconvenient, e.g., under con- ditions of varying ...

reaction step An ELEMENTARY REACTION, constitut- ing one of the stages of a STEPWISE REACTIONin which a reaction INTERMEDIATE(or ...

rearrangement See DEGENERATE REARRANGEMENT; MOLECULAR REARRANGEMENT; SIGMATROPIC REAR- RANGEMENT. rearrangement stage The ELEMEN ...

ENZYMEare available. Generally the active site cavity is defined by comparing the superposition of active to that of inactive mo ...

recommended owing to inconsistency with the terms STEREOSELECTIVITYand STEREOSPECIFICITY. See alsoCHEMOSELECTIVITY. regulation R ...

linked to the quantum mechanical concept of “reso- nance energy.” The term resonanceis also used to refer to the DELOCALIZATIONp ...

Rh blood types A blood group that involves 45 dif- ferent antigens on the surface of red cells that are con- trolled by two clos ...

ribozyme RNA with enzymatic or catalytic ability specifically to cleave (break down) or bind RNA molecules. Also known as autoca ...

FORMATION corresponding to a distinct POTENTIAL- ENERGY minimum), arising from restricted rotation about one single bond. rotati ...

sacrificial anode The ANODEin a CATHODIC PRO- TECTIONsystem. For cathodic protection, a more active metal is placed next to a le ...

saturated fatty acid FATTY ACIDwith a hydrocarbon chain that contains no double bonds but has the maxi- mum possible number of h ...

secondary compound Compounds that are not directly a function in the process of growth and devel- opment in a plant but are norm ...

compound PhX relative to that of a single position in benzene, then the selectivity factor Sf(expressing dis- crimination betwee ...

present in all atoms. The specific radius of each elec- tron shell is determined by the energy level of the elec- trons in that ...

bution is cylindrically symmetrical about the internu- clear axis.) See alsoSIGMA, PI. sigma (σ) constant Specifically, the subs ...

signal transduction pathway Signal transduction refers to the movement of signals from outside the cell to the inside and is a m ...

smelting A process using high temperatures that separates a pure metal, usually in a molten form, from an ore. smog A noxious mi ...

Soddy, Frederick 249 wide-ranging applications from anticancer drugs to nan- otechnology. Fire was also essential for mankind’s ...