isoprene A colourless liquid diene,
CH 2 :C(CH 3 )CH:CH 2 . The systematic
name is 2-methylbuta-1,3-diene. The
isoprene structure is the fundamental structural unit in *terpenes and
natural *rubber. The compound itself
is used in making synthetic rubbers.
isoquinoline See quinoline.
isotactic polymer See polymer.
isotherm 1. A line on a map or
chart joining points or places of
equal temperature. 2. A curve on a
graph representing readings taken at
constant temperature (e.g. the relationship between the pressure and
volume of a gas at constant temperature).
isothermal process Any process
that takes place at constant temperature. In such a process heat is, if necessary, supplied or removed from the
system at just the right rate to maintain constant temperature. Compare
adiabatic process.
isotonic Describing solutions that
have the same osmotic pressure.
isotope One of two or more atoms
of the same element that have the
same number of protons in their nucleus but different numbers of neutrons. Hydrogen (1 proton, no
neutrons), deuterium (1 proton, 1
neutron), and tritium (1 proton, 2
neutrons) are isotopes of hydrogen.
Most elements in nature consist of a
mixture of isotopes. See isotope separation.
isotope separation The separation of the *isotopes of an element
from each other on the basis of slight
differences in their physical properties. For laboratory quantities the
most suitable device is often the
mass spectrometer. On a larger scale
the methods used include gaseous
diffusion (widely used for separating
isotopes of uranium in the form of
the gas uranium hexaÛuoride), distillation (formerly used to produce
heavy water), electrolysis (requiring
cheap electrical power), thermal diffusion (formerly used to separate uranium isotopes, but now considered
uneconomic) and centrifuging. Various laser methods (involving the
excitation of one isotope and its
subsequent separation by electromagnetic means) have also been
employed.
isotopic isomers See isotopomers.
isotopic number (neutron excess)
The difference between the number
of neutrons in an isotope and the
number of protons.
isotopologues Substances that differ only in isotopic composition, e.g.
CH 3 OH, CH 2 DOH, CHD 2 OH, CD 3 OH,
CD 3 OD.
isotopomers (isotopic isomers)
Molecules that have the same numbers of each type of isotopic atom
but in different arrangements in the
molecule. For example, CH 2 DOH and
CH 3 OD are isotopomers.
isotropic Denoting a medium
whose physical properties are independent of direction. Compare
anisotropic.
isozyme (isoenzyme) One of several
forms of an enzyme in an individual
or population that catalyse the same
reaction but differ from each other
in such properties as substrate
afÜnity and maximum rates of enzyme–substrate reaction (see
michaelis–menten curve).
itaconic acid A product of the fermentation of the Ülamentous fungus
Aspergillus niger. Itaconic acid is used
commercially in the production of
adhesives and paints.
IUPAC International Union of Pure
and Applied Chemistry. An internaisoprene
298
i
www.AzShimi.ir www.AzShimi.com
CH 2 :C(CH 3 )CH:CH 2 . The systematic
name is 2-methylbuta-1,3-diene. The
isoprene structure is the fundamental structural unit in *terpenes and
natural *rubber. The compound itself
is used in making synthetic rubbers.
isoquinoline See quinoline.
isotactic polymer See polymer.
isotherm 1. A line on a map or
chart joining points or places of
equal temperature. 2. A curve on a
graph representing readings taken at
constant temperature (e.g. the relationship between the pressure and
volume of a gas at constant temperature).
isothermal process Any process
that takes place at constant temperature. In such a process heat is, if necessary, supplied or removed from the
system at just the right rate to maintain constant temperature. Compare
adiabatic process.
isotonic Describing solutions that
have the same osmotic pressure.
isotope One of two or more atoms
of the same element that have the
same number of protons in their nucleus but different numbers of neutrons. Hydrogen (1 proton, no
neutrons), deuterium (1 proton, 1
neutron), and tritium (1 proton, 2
neutrons) are isotopes of hydrogen.
Most elements in nature consist of a
mixture of isotopes. See isotope separation.
isotope separation The separation of the *isotopes of an element
from each other on the basis of slight
differences in their physical properties. For laboratory quantities the
most suitable device is often the
mass spectrometer. On a larger scale
the methods used include gaseous
diffusion (widely used for separating
isotopes of uranium in the form of
the gas uranium hexaÛuoride), distillation (formerly used to produce
heavy water), electrolysis (requiring
cheap electrical power), thermal diffusion (formerly used to separate uranium isotopes, but now considered
uneconomic) and centrifuging. Various laser methods (involving the
excitation of one isotope and its
subsequent separation by electromagnetic means) have also been
employed.
isotopic isomers See isotopomers.
isotopic number (neutron excess)
The difference between the number
of neutrons in an isotope and the
number of protons.
isotopologues Substances that differ only in isotopic composition, e.g.
CH 3 OH, CH 2 DOH, CHD 2 OH, CD 3 OH,
CD 3 OD.
isotopomers (isotopic isomers)
Molecules that have the same numbers of each type of isotopic atom
but in different arrangements in the
molecule. For example, CH 2 DOH and
CH 3 OD are isotopomers.
isotropic Denoting a medium
whose physical properties are independent of direction. Compare
anisotropic.
isozyme (isoenzyme) One of several
forms of an enzyme in an individual
or population that catalyse the same
reaction but differ from each other
in such properties as substrate
afÜnity and maximum rates of enzyme–substrate reaction (see
michaelis–menten curve).
itaconic acid A product of the fermentation of the Ülamentous fungus
Aspergillus niger. Itaconic acid is used
commercially in the production of
adhesives and paints.
IUPAC International Union of Pure
and Applied Chemistry. An internaisoprene
298
i
www.AzShimi.ir www.AzShimi.com