1-Methylcyclohexene is heated with alkaline $\mathrm{KMnO}{}_4$ and the mixture is acidified. The product is

Cleavage opens the ring at the double bond. The ring carbon with the methyl group has no H and becomes a ketone, $\mathrm{CH}{}_3-\mathrm{CO}{}^{-}$, and the other carbon (one H) becomes $-\mathrm{COOH}$. All seven carbons are retained, giving $\mathrm{CH}{}_3\mathrm{CO}(\mathrm{CH}{}_2){}_4\mathrm{COOH}$, 6-oxoheptanoic acid.