Epoxides are cleaved by acid as are other ethers, but milder conditions are sufficient due to ring strain. The mechanism of acid-catalyzed epoxide opening is complex. They seem to be neither purely SN1 nor SN2, but instead to be midway between these two extremes and to have characteristics of both mechanisms. When both epoxide carbon atoms are either primary or secondary, attack of the nucleophile occurs primarily at the less substituted site, an SN2-like result. On the other hand, when one of the epoxide carbons is tertiary nucleophilic attack occurs primarily at the more substituted site, an SN1-like result. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instructions