110 Redox reactions
110.0.1 Oxidation and reduction
Two important types of reactions in organic chemistry areoxidationandreduction.
Inoxidation reactions,the oxidized speciesloses electron density.
Inreduction reactions,the reduced speciesgains electron density.
Of course, these two actions happen in unison as one species is reduced and the other is
oxidized. The termredoxwas coined from the fragmentsred(reduction) andox(oxidation).
110.0.2 Oxidation
Oxidationwas first observed when oxygen drew electrons off of metals, which were then
referred to as ”oxidized”. (Oxygen is more elecronegative than most other elements.) The
term was then applied later to the part of any reaction where electrons are drawn off.
Other elements that commonly oxidize in organic reactions include halogens like chlorine
and bromine.
110.0.3 Reduction
Reductionof a chemical species results in the gain of electrons for that species. This
does not necessarily include any change in charge; any time an atom increases its electron
density even a little bit it is said to be reduced. For example, if an oxygen is removed from
a carbon and replaced by a hydrogen (assume the oxygen is also bonded to another atom),
the formal charge of the carbon does not change. However, the carbon ”sees” a greater share
of the electrons from the single bond to hydrogen than it did for the single bond to oxygen.
That is because hydrogen is less electronegative than oxygen and gives up its electrons a
bit more easily than oxygen does. So a carbon bonded to hydrogen can take up more of its
electron density than the same carbon bonded to oxygen.