Master epoxide opening under acidic vs basic conditions: where the nucleophile attacks (more vs less substituted), inversion, and anti opening. Includes interactive arrow-pushing + practice.
Base conditions: Nu⁻ attacks less substituted carbon (SN2 steric control)
Acid conditions: Protonate epoxide; Nu attacks more substituted carbon (more positive character)
Stereochemistry: Backside attack → inversion at attacked carbon; anti relationship overall
Common nucleophiles: RO⁻, HO⁻, CN⁻ (base); ROH, H2O, X⁻ (acid)