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

Protonation and loss of water gives the secondary cation $(\mathrm{CH}{}_3){}_2\mathrm{CH}-\mathrm{CH}{}^{+}-\mathrm{CH}{}_3$. A 1,2-hydride shift converts it into the more stable tertiary cation $(\mathrm{CH}{}_3){}_2\mathrm{C}{}^{+}-\mathrm{CH}{}_2\mathrm{CH}{}_3$. Loss of a proton by Saytzeff orientation gives the trisubstituted 2-methylbut-2-ene as the major product.