2-Methylpentane, trivially known as isohexane, is a branched-chain alkane with the molecular formula C<sub>6</sub>H<sub>14</sub>. It is a structural isomer of hexane composed of a methyl group bonded to the second carbon atom in a pentane chain.
As of early 1990s, it was present in American and European gasoline in small amounts, and by 2011 its share in US gas varied between 2 and 8%. Using a quantitative structure-activity relationship (QSAR) prediction model, 2-Methylpentane has a research octane number (RON) of 75, motor octane number (MON) of 77, and cetane number (CN) of 29.