Oxirane Definition:

A cyclic ether containing a three-membered ring system. Also called an epoxide.

Oxirane Explained:

Are three-membered ring structures in which one of the vertices is an oxygen and the other two are carbons. Ring-opening reactions can proceed by either SN2 or SN1 mechanisms, depending on the nature of the epoxide and on the reaction conditions.  If the epoxide is asymmetric, the structure of the product will vary according to which mechanism dominates.   When an asymmetric epoxide undergoes solvolysis in basic methanol, ring-opening occurs by an SN2 mechanism, and the less substituted carbon is the site of nucleophilic attack.