Ph 3 C–CO 2 H + H+→Ph 3 C++ CO + H 2 O(2) The breakdown of a RADICALinto a diamagnetic
molecule or ion and a smaller radical, e.g.,
(CH 3 ) 3 C–O.→(CH 3 ) 2 CO + H 3 C.
[ArBr].–→Ar.+ Br–(solution)(3) The breakdown of a RADICAL IONin a mass spec-
trometer or in solution, forming an ion of lower molar
mass and a radical, e.g.,
[(CH 3 ) 3 C–OH].+→(CH 3 ) 2 COH++
H 3 C.(mass spectrometer)See also HETEROLYTIC BOND-DISSOCIATION
ENERGY.
Frasch process Named for the German-American
chemist Herman Frasch (1851–1914), a method to
extract elemental sulfur by melting the sulfur with super-
heated water (at 170°C under high pressure) and forcing
it to the surface of the Earth as a slurry.
free energy Energy readily available for producing
change in a system.
See alsoGIBBS FREE ENERGY.
free-energy change Determines the direction of
spontaneity of a chemical reaction at constant tempera-
ture. A reaction will proceed to decrease the free energy
of the system.free radical A molecule that contains at least one
unpaired electron; a highly reactive chemical that usu-
ally exists for a short time. Formed in the body during
oxidation, a normal by-product of metabolism, they
can bind with electrons from other molecules and cause
cellular damage by disrupting normal cellular pro-
cesses. They can be kept in check by antioxidants such
as certain enzymes or vitamins (C and E).freezing-point depression The decrease in the freez-
ing point of a solvent caused by the presence of a
solute. The lower the molecular weight, the greater is
the ability of a molecule to depress the freezing point
for any given concentration by weight.frequency The rate at which a periodic event occurs.
The number of repeating corresponding points on a
wave that pass a given observation point per unit time;
the rate at which the waves of electromagnetic radia-
tion pass a point.frontier orbitals The highest-energy occupied molec-
ular orbital (HOMO) (filled or partly filled) and lowest-
energy unoccupied molecular orbital (LUMO)
(completely or partly vacant) of a MOLECULAR ENTITY.
Examination of the mixing of frontier molecular
orbitals of reacting molecular entities affords an
approach to the interpretation of reaction behavior.
This constitutes a simplified perturbation MOLECULAR
ORBITALtheory of chemical behavior.
See alsoLOWEST UNOCCUPIED MOLECULAR ORBIT;
SOMO; SUBJACENT ORBITAL.fuel cell A voltaic cell where reactants are continually
supplied to convert chemical energy to electrical energy.
Typically, the reaction uses H 2 as fuel, reacting electro-
chemically with oxygen to produce water and electrical
energy.112 Frasch process
Frasch process