organo- PreÜx used before the
name of an element to indicate compounds of the elements containing
organic groups (with the element
bound to carbon atoms). For example, lead(IV) tetraethyl is an organolead compound.
organometallic compound A
compound in which a metal atom or
ion is bound to an organic group.
Organometallic compounds may
have single metal–carbon bonds,
as in the aluminium alkyls (e.g.
Al(CH 3 ) 3 ). In some cases, the bonding
is to the pi electrons of a double
bond, as in complexes formed between platinum and ethene, or to
the pi electrons of a ring, as in *ferrocene.
A
• Information about IUPAC nomenclature
• Further information about
nomenclature
organophosphorus compound
A compound that has at least one
carbon–phosphorus bond. Organophosphorus compounds are used as
pesticides (as in malathion and
parathion) and as catalysts and solvents. Phosphate esters, sometimes
included in this category, are employed for Üre-prooÜng textiles.
Orgel diagram A diagram showing
how the energy levels of a transitionmetal atom split when it is placed in
a ligand Üeld. The vertical axis shows
the energy and the horizontal axis
shows the strength of the ligand
Üeld, with zero ligand Üeld strength
at the centre of the horizontal axis.
That the splitting for d
n is the same
as d
n + 5 and the opposite of d
10 – n is
readily seen on an Orgel diagram,
both for octahedral and tetrahedral
Üelds. The spectroscopic, optical, and
magnetic properties of complexes of
transition metals are made clear in
such diagrams. Orgel diagrams are
named after Leslie Orgel, who developed them in 1955.
origin of elements The nuclear
processes that give rise to chemical
elements. There is not one single
process that can account for all the
elements. The abundance of the
chemical elements is determined not
just by the stability of the nuclei of
the atoms but also how readily the
nuclear processes leading to the existence of these atoms occur.
Most of the helium in the universe
was produced by fusion in the early
universe when the temperature and
the pressure were very high. Most of
the elements between helium and
iron were made in nuclear fusion reactions inside stars. Since iron is at
the bottom of the energy valley of
stability, energy needs to be put into
a nucleus heavier than iron for a fusion reaction to occur. Inside stars
some heavy elements are built up by
the s-process, where s stands for
slow, in which high-energy neutrons
are absorbed by a nucleus, with the
resulting nucleus undergoing beta
decay to produce a nucleus with a
higher atomic number. Some heavy
elements are produced by the rprocess, where r stands for rapid,
which occurs in supernova explosions when a great deal of gravitational energy is released when a
large star that has exhausted its nuclear fuel collapses to a neutron star,
with the release of a very large number of neutrons.
ornithine (Orn) An *amino acid,
H 2 N(CH 2 ) 3 CH(NH 2 )COOH, that is not
a constituent of proteins but is important in living organisms as an intermediate in the reactions of the
*urea cycle and in arginine synthesis.
ornithine cycle See urea cycle.
orpiment A natural yellow mineral
form of arsenic(III) sulphide, As 2 S 3 .
389
orpiment
o
www.AzShimi.ir www.AzShimi.com
name of an element to indicate compounds of the elements containing
organic groups (with the element
bound to carbon atoms). For example, lead(IV) tetraethyl is an organolead compound.
organometallic compound A
compound in which a metal atom or
ion is bound to an organic group.
Organometallic compounds may
have single metal–carbon bonds,
as in the aluminium alkyls (e.g.
Al(CH 3 ) 3 ). In some cases, the bonding
is to the pi electrons of a double
bond, as in complexes formed between platinum and ethene, or to
the pi electrons of a ring, as in *ferrocene.
A
• Information about IUPAC nomenclature
• Further information about
nomenclature
organophosphorus compound
A compound that has at least one
carbon–phosphorus bond. Organophosphorus compounds are used as
pesticides (as in malathion and
parathion) and as catalysts and solvents. Phosphate esters, sometimes
included in this category, are employed for Üre-prooÜng textiles.
Orgel diagram A diagram showing
how the energy levels of a transitionmetal atom split when it is placed in
a ligand Üeld. The vertical axis shows
the energy and the horizontal axis
shows the strength of the ligand
Üeld, with zero ligand Üeld strength
at the centre of the horizontal axis.
That the splitting for d
n is the same
as d
n + 5 and the opposite of d
10 – n is
readily seen on an Orgel diagram,
both for octahedral and tetrahedral
Üelds. The spectroscopic, optical, and
magnetic properties of complexes of
transition metals are made clear in
such diagrams. Orgel diagrams are
named after Leslie Orgel, who developed them in 1955.
origin of elements The nuclear
processes that give rise to chemical
elements. There is not one single
process that can account for all the
elements. The abundance of the
chemical elements is determined not
just by the stability of the nuclei of
the atoms but also how readily the
nuclear processes leading to the existence of these atoms occur.
Most of the helium in the universe
was produced by fusion in the early
universe when the temperature and
the pressure were very high. Most of
the elements between helium and
iron were made in nuclear fusion reactions inside stars. Since iron is at
the bottom of the energy valley of
stability, energy needs to be put into
a nucleus heavier than iron for a fusion reaction to occur. Inside stars
some heavy elements are built up by
the s-process, where s stands for
slow, in which high-energy neutrons
are absorbed by a nucleus, with the
resulting nucleus undergoing beta
decay to produce a nucleus with a
higher atomic number. Some heavy
elements are produced by the rprocess, where r stands for rapid,
which occurs in supernova explosions when a great deal of gravitational energy is released when a
large star that has exhausted its nuclear fuel collapses to a neutron star,
with the release of a very large number of neutrons.
ornithine (Orn) An *amino acid,
H 2 N(CH 2 ) 3 CH(NH 2 )COOH, that is not
a constituent of proteins but is important in living organisms as an intermediate in the reactions of the
*urea cycle and in arginine synthesis.
ornithine cycle See urea cycle.
orpiment A natural yellow mineral
form of arsenic(III) sulphide, As 2 S 3 .
389
orpiment
o
www.AzShimi.ir www.AzShimi.com