Heating 3,3-dimethylbutan-2-ol with concentrated $\mathrm{H}{}_2\mathrm{SO}{}_4$ gives mainly (Saytzeff product after carbocation rearrangement):

Protonation and loss of water give the secondary 3,3-dimethylbutan-2-yl cation. A 1,2-methyl shift gives the tertiary 2,3-dimethylbutan-2-yl cation. Loss of a proton from the more substituted side gives the tetrasubstituted 2,3-dimethylbut-2-ene as the major product.