bitals in a molecule: the *highest occupied molecular orbital (HOMO) and
the *lowest unoccupied molecular
orbital (LUMO). These two molecular
orbitals are usually the most important ones in determining chemical
and spectroscopic properties of the
molecule.
frontier-orbital theory A theory
of the reactions of molecules that
emphasizes the energies and symmetries of *frontier orbitals. Frontier orbital theory was developed by the
Japanese chemist Kenichi Fukui
(1919–98) in the 1950s and is an alternative approach to the *Woodward–Hoffmann rules. It has been
very successful in explaining such reactions as the *Diels–Alder reaction.
Frost diagram A graph showing
how standard electrode potentials
vary with oxidation state for different oxidation states of an element.
Frost diagrams can be constructed
from *Latimer diagrams. For an element M, the standard electrode potential E Š is calculated for the
reaction.
M(N) + Ne
–
→ M(0)
where M(N) indicates the species in
oxidation state N and M(0) indicates
the zero oxidation state. The Frost diagram is then obtained by plotting
NEŠ against N for the different
species. NEŠ is proportional to the
standard Gibbs free energy of the
particular half reaction.
In a Frost diagram, the lowest
point corresponds to the most stable
oxidation state of the element. Also,
the slope of a line between two
points is the standard potential of
the couple represented by the points.
Like Latimer diagrams, Frost diagrams depend on pH.
froth Ûotation A method of separating mixtures of solids, used industrially for separating ores from the
unwanted gangue. The mixture is
ground to a powder and water and a
frothing agent added. Air is blown
through the water. With a suitable
frothing agent, the bubbles adhere
only to particles of ore and carry
them to the surface, leaving the
gangue particles at the bottom.
fructose (fruit sugar; laevulose) A
simple sugar, C 6 H 12 O 6 , stereoisomeric with glucose (see monosaccharide). (Although natural fructose is
the d-form, it is in fact laevorotatory.)
Fructose occurs in green plants,
fruits, and honey and tastes sweeter
than sucrose (cane sugar), of which it
is a constituent. Derivatives of fructose are important in the energy metabolism of living organisms. Some
polysaccharide derivatives (fructans)
are carbohydrate energy stores in
certain plants.
fructose 1,6-bisphosphate An intermediate formed in the initial stage
of *glycolysis by the phosphorylation
of glucose using ATP.
fruit sugar See fructose.
FT-IR See fourier-transform infrared.
5-FU See 5-fluorouracil.
fuel A substance that is oxidized or
otherwise changed in a furnace or
heat engine to release useful heat or
energy. For this purpose wood, vegetable oil, and animal products have
largely been replaced by *fossil fuels
since the 18th century.
The limited supply of fossil fuels
and the expense of extracting them
from the earth has encouraged the
development of nuclear fuels to produce electricity.
fuel cell A cell in which the chemical energy of a fuel is converted directly into electrical energy. The
simplest fuel cell is one in which hydrogen is oxidized to form water
237
fuel cell
f
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the *lowest unoccupied molecular
orbital (LUMO). These two molecular
orbitals are usually the most important ones in determining chemical
and spectroscopic properties of the
molecule.
frontier-orbital theory A theory
of the reactions of molecules that
emphasizes the energies and symmetries of *frontier orbitals. Frontier orbital theory was developed by the
Japanese chemist Kenichi Fukui
(1919–98) in the 1950s and is an alternative approach to the *Woodward–Hoffmann rules. It has been
very successful in explaining such reactions as the *Diels–Alder reaction.
Frost diagram A graph showing
how standard electrode potentials
vary with oxidation state for different oxidation states of an element.
Frost diagrams can be constructed
from *Latimer diagrams. For an element M, the standard electrode potential E Š is calculated for the
reaction.
M(N) + Ne
–
→ M(0)
where M(N) indicates the species in
oxidation state N and M(0) indicates
the zero oxidation state. The Frost diagram is then obtained by plotting
NEŠ against N for the different
species. NEŠ is proportional to the
standard Gibbs free energy of the
particular half reaction.
In a Frost diagram, the lowest
point corresponds to the most stable
oxidation state of the element. Also,
the slope of a line between two
points is the standard potential of
the couple represented by the points.
Like Latimer diagrams, Frost diagrams depend on pH.
froth Ûotation A method of separating mixtures of solids, used industrially for separating ores from the
unwanted gangue. The mixture is
ground to a powder and water and a
frothing agent added. Air is blown
through the water. With a suitable
frothing agent, the bubbles adhere
only to particles of ore and carry
them to the surface, leaving the
gangue particles at the bottom.
fructose (fruit sugar; laevulose) A
simple sugar, C 6 H 12 O 6 , stereoisomeric with glucose (see monosaccharide). (Although natural fructose is
the d-form, it is in fact laevorotatory.)
Fructose occurs in green plants,
fruits, and honey and tastes sweeter
than sucrose (cane sugar), of which it
is a constituent. Derivatives of fructose are important in the energy metabolism of living organisms. Some
polysaccharide derivatives (fructans)
are carbohydrate energy stores in
certain plants.
fructose 1,6-bisphosphate An intermediate formed in the initial stage
of *glycolysis by the phosphorylation
of glucose using ATP.
fruit sugar See fructose.
FT-IR See fourier-transform infrared.
5-FU See 5-fluorouracil.
fuel A substance that is oxidized or
otherwise changed in a furnace or
heat engine to release useful heat or
energy. For this purpose wood, vegetable oil, and animal products have
largely been replaced by *fossil fuels
since the 18th century.
The limited supply of fossil fuels
and the expense of extracting them
from the earth has encouraged the
development of nuclear fuels to produce electricity.
fuel cell A cell in which the chemical energy of a fuel is converted directly into electrical energy. The
simplest fuel cell is one in which hydrogen is oxidized to form water
237
fuel cell
f
www.AzShimi.ir www.AzShimi.com