The regioselectivity in the opening of asymmetric epoxides depends on the reaction conditions.:
Under basic conditions, nucleophilic attack occurs at the less hindered carbon of the epoxide ring, driven by steric factors, resulting in the formation of the more substituted alcohol.
Under acidic conditions, the epoxide undergoes protonation, forming a positively charged oxygen atom. The nucleophile attacks the carbon bearing the positive charge, leading to the formation of the less substituted alcohol.