1-Cyclobutylethanol, $\mathrm{CH}{}_3-\mathrm{CH}(\mathrm{OH})-\mathrm{C}{}_4\mathrm{H}{}_7$ (cyclobutyl ring attached at the carbinol carbon), is heated with concentrated $\mathrm{H}{}_2\mathrm{SO}{}_4$. The major alkene is

Loss of water gives the secondary cation next to a strained four-membered ring. Migration of a ring C-C bond to the cationic carbon expands the ring to a cyclopentyl cation, relieving strain. A hydride shift from the adjacent CH(CH3) then gives the tertiary 1-methylcyclopentyl cation, which loses a proton to give 1-methylcyclopentene.