Illustrated Glossary of Organic Chemistry

Reduction: (1) Any process in which there is a increase in the number of covalent bonds between an atom and atom(s) that are less electronegative. Commonly seen as, but not limited to, increasing the number of bonds between carbon and hydrogen.


Reaction of sodium borohydride with acetone is a reduction because there is an increase (from zero to one) in the number of bonds between carbon (EN = 2.5) and hydrogen (EN = 2.1), and also between oxygen (EN = 3.5) and hydrogen (EN = 2.1).


Catalytic hydrogenation of propene is a reduction because there is an increase (from three to five) in the number of bonds between carbon (EN = 2.5) and hydrogen (EN = 2.1).


Combustion of methane is an oxidation because there is an increase (from zero to four) in number of bonds between carbon (EN = 2.5) and oxygen (EN = 3.5).


Free radical halogenation of methane is an oxidation because there is an increase (from zero to one) in the number of bonds between carbon (EN = 2.5) and bromine (EN = 2.8).

(2) Any process in which formal charge is made more negative (less positive) by adding electrons.

In the production of iron from hematite (Fe2O3), Fe3+ is reduced to Fe0 and carbon is oxidized to CO2.