3-Methylbutan-2-ol is heated with concentrated $\mathrm{HBr}$. The principal bromide formed is

Protonation of the hydroxyl group and loss of water give the secondary cation $(\mathrm{CH}{}_3){}_2\mathrm{CH}-\mathrm{CH}{}^{+}-\mathrm{CH}{}_3$. A 1,2-hydride shift gives the more stable tertiary cation $(\mathrm{CH}{}_3){}_2\mathrm{C}{}^{+}-\mathrm{CH}{}_2\mathrm{CH}{}_3$, which is captured by bromide to give 2-bromo-2-methylbutane.