3-Methylbutan-2-ol is heated with concentrated $\mathrm{H}{}_2\mathrm{SO}{}_4$ at 440 K. The major alkene is

The secondary alcohol ionises (E1) to the secondary cation $\mathrm{CH}{}_3-\mathrm{CH}{}^{+}-\mathrm{CH}(\mathrm{CH}{}_3){}_2$. A 1,2-hydride shift converts it into the tertiary cation $\mathrm{CH}{}_3-\mathrm{CH}{}_2-\mathrm{C}{}^{+}(\mathrm{CH}{}_3){}_2$, which loses a proton mainly from the CH2 group (Saytzeff) to give 2-methylbut-2-ene.