Organic Chemistry/Introduction to reactions/Redox reactions

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Oxidation and reduction

Two important types of reactions in organic chemistry are oxidation and reduction.

In oxidation reactions, the oxidized species loses electron density.

In reduction reactions, the reduced species gains electron density.

Of course, these two actions happen in unison as one species is reduced and the other is oxidized. The term redox was coined from the fragments red (reduction) and ox (oxidation).

Oxidation

Oxidation was 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.

Reduction

Reduction of 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.

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