Addition reaction

An addition reaction combines atoms or groups with a molecule, often across a multiple bond, without eliminating another group.

Electrophilic addition: An addition to a multiple bond initiated when an electron-poor species accepts electron density. This common alkene pathway begins when an electrophile attacks the bond.
Alkene: A hydrocarbon containing at least one carbon–carbon double bond. Alkenes are the standard substrates for additions across a carbon–carbon π bond.
Hydrogenation: A reaction that adds hydrogen to a substance, commonly reducing carbon–carbon multiple bonds. It converts alkenes and alkynes into more saturated compounds by hydrogen addition.
Elimination reaction: A reaction that removes atoms or groups from a molecule, often forming a multiple bond. Elimination commonly reverses addition by restoring a π bond and expelling a group.
Nucleophilic addition: An addition in which a nucleophile attacks an electron-deficient center, often a carbonyl carbon. Carbonyl compounds undergo addition because their polarized C=O bond has an electrophilic carbon.
Alkyne: A hydrocarbon containing at least one carbon–carbon triple bond. Alkynes can undergo addition across one or both components of their triple bond.
Halogenation: A reaction that introduces one or more halogen atoms into a molecule. Adding halogens across an alkene is a standard route to vicinal dihalides.
Substitution reaction: A reaction in which one atom or group in a molecule is replaced by another. Unlike addition, substitution replaces a group rather than combining groups across a bond.
Radical addition: An addition in which a radical forms a new bond to a molecule, generating another radical intermediate. Radical chains enable additions that do not follow ionic alkene mechanisms.
Carbonyl group: A functional group consisting of a carbon atom double-bonded to an oxygen atom. Its polarized double bond makes carbonyl compounds susceptible to nucleophilic addition.

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