Classification of organic reactions

Many reactions of organic molecules result in a change in the functional group, but no change in the hydrocarbon skeleton.

Classifying organic reactions by type highlights similarities between systems that may at first appear different, and makes learning reaction chemistry easier. The three classifications below are based on structural relationships between the organic reactant and the organic product.

addition

Two parts of a reagent (One of the reactants in a reaction. In organic chemistry the reagent is the nonorganic reactant.) molecule are added across an unsaturation (multiple bond) to give an organic product that has one less unsaturation (multiple bond) than the organic reactant.

CH₂=CH₂ + Br–Br

Br–CH₂–CH₂–Br
CH₂=CH₂ + H–H

H-CH₂–CH₂–H
CH₂=CH₂ + H–Br

H-CH₂–CH₂–Br

CH₂=CH₂ + H–OH

H⁺(aq)

H-CH₂–CH₂–OH

elimination

This is the opposite to addition as the components of a molecule are removed from adjacent carbon atoms, and the organic product has one more unsaturation than the organic reactant.

H–CH₂–CH₂–Br + OH^–

CH₂=CH₂+ H–OH + Br^–

substitution

A part of an organic molecule is exchanged with a part of the reagent (One of the reactants in a reaction. In organic chemistry the reagent is the nonorganic reactant.).

CH₃CH₂–Br + OH^–

CH₃CH₂–OH + Br^–