chemical conformations are opposite
(i.e. 1R,2S or 1S,1R) the name
ephedrine is used. If the conformations are the same (1R,2R or 1S,2S)
then the compound is called pseudoephedrine.
epimerism A type of optical isomerism 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.
epinephrine See adrenaline.
epitaxy (epitaxial growth) Growth
of a layer of one substance on a single 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 devices.
EPM See electron probe microanalysis.
epoietin (EPO) A hormone that regulates the production of red blood
cells in the body. The drug is used
medically to treat anemia, and is also
used illegally by athletes participating in endurance events.
epoxides Compounds 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
CH 3
C
H 3
C
H 3
Epoxides
epoxyethane (ethylene oxide) A
colourless Ûammable 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 catalytic 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. in Üre Üghting).
epoxy resins Synthetic resins produced by copolymerizing epoxide
compounds with phenols. They contain –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 further polymerization of the resin.
Epoxy resins are used in electrical
equipment and in the chemical industry (because of resistance to
chemical attack). They are also used
as adhesives.
EPR See electron paramagnetic
resonance.
epsomite A mineral form of *magnesium sulphate heptahydrate,
MgSO 4 .7H 2 O.
Epsom salt See magnesium sulphate.
equation of state An 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 volume occupied by the gas molecules
(according to this law if the pressure
is inÜnitely great the volume becomes zero), nor does it take into account 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 attractive forces between particles, and nb
is the volume occupied by the particles themselves when the pressure is
www.AzShimi.ir www.AzShimi.com
(i.e. 1R,2S or 1S,1R) the name
ephedrine is used. If the conformations are the same (1R,2R or 1S,2S)
then the compound is called pseudoephedrine.
epimerism A type of optical isomerism 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.
epinephrine See adrenaline.
epitaxy (epitaxial growth) Growth
of a layer of one substance on a single 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 devices.
EPM See electron probe microanalysis.
epoietin (EPO) A hormone that regulates the production of red blood
cells in the body. The drug is used
medically to treat anemia, and is also
used illegally by athletes participating in endurance events.
epoxides Compounds 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
CH 3
C
H 3
C
H 3
Epoxides
epoxyethane (ethylene oxide) A
colourless Ûammable 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 catalytic 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. in Üre Üghting).
epoxy resins Synthetic resins produced by copolymerizing epoxide
compounds with phenols. They contain –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 further polymerization of the resin.
Epoxy resins are used in electrical
equipment and in the chemical industry (because of resistance to
chemical attack). They are also used
as adhesives.
EPR See electron paramagnetic
resonance.
epsomite A mineral form of *magnesium sulphate heptahydrate,
MgSO 4 .7H 2 O.
Epsom salt See magnesium sulphate.
equation of state An 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 volume occupied by the gas molecules
(according to this law if the pressure
is inÜnitely great the volume becomes zero), nor does it take into account 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 attractive forces between particles, and nb
is the volume occupied by the particles themselves when the pressure is
www.AzShimi.ir www.AzShimi.com