Chemistry – Organic chemistry - Alkanes | e-Consult

A substitution reaction is a type of chemical reaction where one atom or group of atoms in a molecule is replaced by another atom or group of atoms.

Example 1: Halogenation of Alkanes: In the reaction of an alkane (like methane, CH₄) with a halogen (like chlorine, Cl₂) in the presence of UV light, one hydrogen atom is replaced by a halogen atom.

CH₄(g) + Cl₂(g) → CH₃Cl(g) + HCl(g)

Example 2: Hydrohalogenation of Alkenes: An alkene (like ethene, C₂H₄) reacts with a hydrogen halide (like hydrochloric acid, HCl) to replace a hydrogen atom on the alkene with a hydrogen halide group.

C₂H₄(g) + HCl(g) → CH₃Cl(g)

In both examples, a specific atom or group of atoms is directly replaced by another.