2,3-Dimethylbutane-2,3-diol is treated with dilute $\mathrm{H}{}_2\mathrm{SO}{}_4$ and warmed (pinacol rearrangement). The product is:

Protonation and loss of water from one OH gives the tertiary cation $(\mathrm{CH}{}_3){}_2\mathrm{C}{}^{+}-\mathrm{C}(\mathrm{CH}{}_3){}_2\mathrm{OH}$. A methyl group migrates from the carbinol carbon to the cationic carbon, giving the oxocarbenium ion $(\mathrm{CH}{}_3){}_3\mathrm{C}-\mathrm{C}{}^{+}(\mathrm{CH}{}_3)-\mathrm{OH}$. Loss of $\mathrm{H}{}^{+}$ from OH gives $(\mathrm{CH}{}_3){}_3\mathrm{C}-\mathrm{CO}-\mathrm{CH}{}_3$.