Substitution in the context of organic chemistry has the general meaning of replacing an atom, a functional group, or a substituent in a molecule.

Substituted compounds

Substituted compounds are chemical compounds where one or more hydrogen atoms of a core structure have been replaced with a functional group like alkyl, hydroxy, or halogen.

Example

Benzene is a simple aromatic ring. Subsituted benzenes are a heterogeneous group of chemicals with a wide spectrum of uses and properties:

• benzene C₆H₆
• toluene C₆H₅-CH₃
• xylene C₆H₄(-CH₃)₂
• mesitylene C₆H₃(-CH₃)₃
• phenol C₆H₅-OH
• aniline C₆H₅-NH₂
• chlorobenzene C₆H₅-Cl
• nitrobenzene C₆H₅-NO₂
• benzoic acid C₆H₅-COOH
• picric acid C₆H₂(-OH)(-NO₂)₃
• trinitrotoluene C₆H₂(-CH₃)(-NO₂)₃
• salicylic acid C₆H₄(-OH)(-COOH)
• acetylsalicylic acid C₆H₄(-O-C(=O)-CH₃)(-COOH)
• paracetamol C₆H₄(-NH-C(=O)-CH₃)(-OH)
• phenacetin C₆H₄(-NH-C(=O)-CH₃)(-O-CH₂-CH₃)

Substitution reaction

A substitution reaction is a general type of organic reaction where one functional group or substituent in the reactant molecule is replaced by another. Common types of substitution reactions are:

• nucleophilic substitution.
• halogenation