Dictionary of Chemistry [6th Ed.]

chemical conformations are opposite

(i.e. 1R,2S or 1S,1R) the name

ephedrine is used. If the conforma-

tions are the same (1R,2R or 1S,2S)

then the compound is called pseu-

doephedrine.

epimerismA type of optical iso-

merism in which a molecule has two

chiral centres; two optical isomers

(epimers) differ in the arrangement

about one of these centres. See also

optical activity.

epinephrineSee adrenaline.

epitaxy(epitaxial growth) Growth

of a layer of one substance on a sin-

gle crystal of another, such that the

crystal structure in the layer is the

same as that in the substrate. It is

used in making semiconductor de-

vices.

EPMSee electron probe micro-

analysis.

epoietin(EPO)A hormone that reg-

ulates the production of red blood

cells in the body. The drug is used

medically to treat anemia, and is also

used illegally by athletes participat-

ing in endurance events.

epoxidesCompounds that contain

oxygen atoms in their molecules as

part of a three-membered ring (see

formula). Epoxides are thus cyclic

ethers.

epimerism 208

e

O

CH 3

3 CH CH 3

3 CH

Epoxides

epoxyethane(ethylene oxide)A

colourlessÛammable gas, C 2 H 4 O;

m.p. –111°C; b.p. 13.5°C. It is a cyclic

ether (see epoxides), made by the cat-

alytic oxidation of ethene. It can be

hydrolysed to ethane-1,2-diol and

also polymerizes to ...-OC 2 H 4 -O-C 2 H 4 -

..., which is used for lowering the

viscosity of water (e.g. inÜreÜght-

ing).

epoxy resins Synthetic resins pro-

duced by copolymerizing epoxide

compounds with phenols. They con-

tain –O– linkages and epoxide groups

and are usually viscous liquids. They

can be hardened by addition of

agents, such as polyamines, that

form cross-linkages. Alternatively,

catalysts may be used to induce fur-

ther polymerization of the resin.

Epoxy resins are used in electrical

equipment and in the chemical in-

dustry (because of resistance to

chemical attack). They are also used

as adhesives.

EPRSee electron paramagnetic

resonance.

epsomiteA mineral form of *mag-

nesium sulphate heptahydrate,

MgSO 4 .7H 2 O.

Epsom saltSee magnesium sul-

phate.

equation of stateAn equation

that relates the pressure p, volume V,

and thermodynamic temperature T

of an amount of substance n. The

simplest is the ideal *gas law:

pV = nRT,

where R is the universal gas constant.

Applying only to ideal gases, this

equation takes no account of the vol-

ume occupied by the gas molecules

(according to this law if the pressure

is inÜnitely great the volume be-

comes zero), nor does it take into ac-

count any forces between molecules.

A more accurate equation of state

would therefore be

(p + k)(V – nb) = nRT,

where k is a factor that reÛects the

decreased pressure on the walls of

the container as a result of the attrac-

tive forces between particles, and nb

is the volume occupied by the parti-

cles themselves when the pressure is