An epoxide is a type of cyclic ether characterized by a three-membered ring that includes an oxygen atom.

Epoxides are typically formed through the reaction of an alkene with either a peroxide or a halohydrin. When a peroxide is involved, the alkene undergoes a free radical addition reaction, resulting in the formation of a cyclic intermediate. This intermediate then rearranges to yield the epoxide. In contrast, when a halohydrin is used, the alkene first reacts via electrophilic addition to create a halohydrin intermediate. This intermediate subsequently undergoes intramolecular nucleophilic substitution, leading to the formation of the epoxide.

Epoxides play a crucial role as intermediates in organic synthesis and are utilized in the production of a wide array of chemicals, including solvents, adhesives, and plastics. Additionally, they serve as important reagents in organic chemistry, particularly for synthesizing cyclic compounds. Due to the inherent ring strain associated with their three-membered structure, epoxides exhibit high reactivity. They can participate in various chemical reactions, such as ring-opening, nucleophilic addition, and rearrangement reactions. This reactivity renders epoxides valuable in numerous applications, including their use as catalysts and intermediates in the synthesis of pharmaceuticals.