What type of reaction would be expected when an alkene reacts with a peracid?

When an alkene reacts with a peracid, the reaction that occurs is epoxidation. This process involves the addition of an oxygen atom across the double bond of the alkene, resulting in the formation of an epoxide, which is a three-membered cyclic ether. The mechanism proceeds through the formation of a cyclic peracid-alkene complex that leads to the creation of the epoxide by concerted intramolecular transfer of an oxygen atom.

This reaction is stereospecific and retains the configuration of the alkene in the resulting epoxide. The characteristic feature of this reaction is the formation of the epoxide ring, which is a significant functional group in organic chemistry due to its reactivity and usefulness in further chemical transformations. The use of peracids, such as m-chloroperbenzoic acid (MCPBA), is common in this context because they are effective at converting alkenes into epoxides without needing additional reagents or catalysts.