2-Methyloxirane is opened by each of the following under basic or neutral nucleophilic conditions. In which cases does the nucleophile bond to the $\mathrm{CH}{}_2$ carbon of the ring (less hindered carbon)?

Cyanide, azide and hydride open the ring by a pure SN2 process and therefore attack the less hindered $\mathrm{CH}{}_2$ carbon. This gives 3-hydroxybutanenitrile, 1-azidopropan-2-ol and propan-2-ol respectively. In acidic methanol the more substituted carbon bears more positive charge and the attack there is favoured.