oxacycles

Oxacycles are heterocycles that contain one or more oxygen atoms in a ring. When the ring contains a single oxygen atom, it is often described using the oxacyclo nomenclature, with the ring size indicated. For example, oxacyclopentane denotes a five-membered oxacycle and oxacyclohexane denotes a six-membered oxacycle.

Common examples include oxacyclopentane, known as tetrahydrofuran (THF), a five-membered oxacycle, and oxacyclohexane, known as tetrahydropyran (THP), a six-membered oxacycle. Rings with two or more oxygen atoms are called dioxacycles; for instance, 1,4-dioxane is a six-membered dioxacycle. Oxacycles span a range of ring sizes and substitution patterns, making them a versatile class in organic chemistry.

Properties of oxacycles are influenced by ring size and substitution. They are typically polar due to the ether oxygen, and five- and six-membered rings often balance stability with useful reactivity. Their chemistry overlaps with that of other heterocycles, and they frequently appear as solvents, intermediates, or scaffolds in pharmaceuticals and materials science. Crown ethers and related polyether rings are related families that extend the concept to larger cyclic ethers capable of ion binding.

Synthesis of oxacycles generally involves intramolecular ether formation or cyclization of diols, among other cyclization strategies. The resulting compounds range from simple solvents, such as THF, to more complex polyether frameworks used in synthesis and catalysis. Safety considerations include flammability for many oxacyclic ethers and, for some dioxanes, potential health concerns requiring careful handling. See also heterocycles; crown ethers; oxacycles in polymer chemistry.