A substitution reaction is a type of chemical reaction where an atom or functional group of a molecule is replaced by another atom or functional group. It is a reaction that involves the replacement of one atom or molecule of a compound with another atom or molecule.
An example of a substitution reaction is the conversion of methane to carbon tetrachloride, where hydrogen atoms are replaced by chlorine atoms. Another example is the reaction of ethanol with hydrogen iodide, where the hydroxyl group of ethanol is replaced by iodine to form iodoethane and water.
Substitution reactions are of two types: nucleophilic reactions and electrophilic reactions. In nucleophilic reactions, the atom is an electron-rich species, while in electrophilic reactions, the atom is an electron-deficient species. Examples of nucleophilic reagents are the halogen anions, ammonia, the hydroxyl group, the alkoxy group, the cyano group, and the hydrosulfide group. In electrophilic substitution, the electron pair for bonding with the substrate comes from the substrate itself.
Substitution reactions are widely used in organic chemistry and have many applications. Some of the organic reactions that use the mechanism of substitution reaction include Williamson ether synthesis, Friedel-Crafts acylation, Friedel-Crafts alkylation, halogenation, and Fischer esterification.
