zum Directory-modus

Introduction to Oxidation and Reduction

Oxidation Numbers

Three rules are applied to calculate the oxidation number of carbon in organic compounds.

Rule No.1
Bonds are broken heterolytically in a formal manner taking into account the electronegativity of the atoms.
Fig.1
Heterolytic cleavage of bonds
Bonding electrons are assigned entirely to the more electronegative atom.
Rule No.2
Covalent bonds between atoms of the same type are broken homolytically.
Fig.2
Homolytic cleavage of bonds
Rule No 3
The formal charge of the atoms thus arrived at corresponds to the oxidation number. The sum of the oxidation numbers represents the total charge of the molecule.
Fig.3
Methane

The oxidation number of carbon in methane is -4.

Fig.4
Ethane

The oxidation number of carbon in ethane is -3.

In complex organic compounds, differently substituted carbon atoms can exhibit different oxidation numbers. Therefore, the definition of oxidation and reduction when applied to a full molecule can be simplified as follows:

Simplified definition of the oxidation and reduction terms
Oxidation: The oxidation number of carbon atoms increases
Reduction: The oxidation number of carbon atoms decreases.
Fig.5
More examples
Page 2 of 8