"Epoxides (oxiranes) are widely used as versatile synthetic intermediates because regio- and stereoselective methods exist both for their construction and subsequent reactions. Reactions of epoxides are dominated by the electrophilic nature of the strained three-membered ring, which is susceptible to attack by a variety of nucleophiles. … The reaction of alkenes with peroxy acids provides for convenient and selective oxidation of double bonds. … Epoxidation involves an electrophilic syn-addition of the oxygen moiety of the peroxy acid to the double bond. The concerted formation of two new C-O bonds ensures that the reaction is stereospecific: cis-alkenes furnish the corresponding cis-epoxides and trans-alkenes the corresponding trans-isomers (racemic)."