Illustrated Glossary of Organic Chemistry

Reduction reaction: A chemical reaction in which reduction occurs. Commonly seen as, but not limited to, decreasing the number of bonds between carbon and oxygen.

Reaction of sodium borohydride with acetone is a reduction reaction 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 reaction because there is an increase (from three to five) in the number of bonds between carbon (EN = 2.5) and hydrogen (EN = 2.1).


Production of iron from hematite (Fe₂O₃) is a reduction reaction because Fe³⁺ is reduced to Fe⁰.


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