an alkane, CH, existing in several isomeric forms: the normal isomer is used in standard mixtures to test octane ratings
See heptane in American Heritage Dictionary 4
(hĕpˈtānˌ)
noun
A volatile, colorless, highly flammable liquid hydrocarbon, C7H16, obtained in the fractional distillation of petroleum and used as a standard in determining octane ratings, as an anesthetic, and as a solvent.