2,2-Dimethyloxirane is treated with $\mathrm{LiAlH}{}_4$ in ether and then with aqueous acid. The product is

With a strong nucleophile in basic medium, ring opening is $\mathrm{S}{}_{\mathrm{N}}2$ and the nucleophile attacks the less hindered carbon. Hydride therefore adds to the $\mathrm{CH}{}_2$ carbon, leaving oxygen on the tertiary carbon. After protonation the product is $(\mathrm{CH}{}_3){}_3\mathrm{C}-\mathrm{OH}$, 2-methylpropan-2-ol.