2-Bromo-3-methylbutane, $(\mathrm{CH}{}_3){}_2\mathrm{CH}-\mathrm{CHBr}-\mathrm{CH}{}_3$, is warmed in water. The main alcohol obtained is

Ionisation gives the secondary cation $(\mathrm{CH}{}_3){}_2\mathrm{CH}-\mathrm{CH}{}^{+}-\mathrm{CH}{}_3$. A 1,2-hydride shift from the adjacent tertiary C-H gives the more stable tertiary cation $(\mathrm{CH}{}_3){}_2\mathrm{C}{}^{+}-\mathrm{CH}{}_2\mathrm{CH}{}_3$, which is trapped by water to give 2-methylbutan-2-ol.