4.3 Oxidation–Reduction Reactions

LEARNING GOALS

After   Chapter 4.3,    you will    be  able    to:

Recall  common  oxidizing   agents  and the characteristics of  a   good    oxidizing   agent

Recall  common  reducing    agents  and the characteristics of  a   good    reducing    agent

Order   a   given   list    of  molecules   from    most    oxidized    to  least   oxidized:

Another important class of reactions are oxidation–reduction (redox) reactions, in which the
oxidation states of the reactants change. Oxidation state is an indicator of the hypothetical charge
that an atom would have if all bonds were completely ionic. Oxidation state can be calculated from
the molecular formula for a molecule. For example, the carbon in methane (CH 4 ) has an oxidation
state of –4 because the hydrogens each have an oxidation state of +1. This is the most reduced form
of carbon. In carbon dioxide (CO 2 ), each of the oxygen atoms has an oxidation state of –2, and the
carbon has an oxidation state of +4. This is the most oxidized form of carbon. For an ion, the
oxidation state is simply the charge—so Na+ and S2– would have oxidation states of +1 and –2,
respectively. Carboxylic acids are more oxidized than aldehydes, ketones, and imines, which in turn
are more oxidized than alcohols, alkyl halides, and amines.

We won’t need to know too much about how to assign oxidation states in organic chemistry, but
should know the definitions of oxidation and reduction. Oxidation refers to an increase in oxidation
state, which means a loss of electrons. In organic chemistry, it is often easier to view oxidation as
increasing the number of bonds to oxygen or other heteroatoms (atoms besides carbon and