2-Methyl-2-butene, 2m2b, 2-methylbut-2-ene, beta-isoamylene, or trimethylethylene is an alkene hydrocarbon with the molecular formula C<sub>5</sub>H<sub>10</sub>. It is a flammable liquid.
Used as a free radical scavenger in trichloromethane and dichloromethane. It is also used to scavenge hypochlorous acid (HOCl) in the Pinnick oxidation.
John Snow, the English physician, experimented with it in the 1840s as an anesthetic.