n-Heptane is the straight-chain
alkane with the
chemical formula H
3C(CH
2)
5CH
3 or C
7H
16. When used as a test fuel component in anti-knock test engines, a 100% heptane fuel is the zero point of the
octane rating scale (the 100 point is a 100%
iso-octane). Octane number equates to the anti-knock qualities of a comparison mixture of heptane and isooctane which is expressed as the percentage of isooctane in heptane and is listed on pumps for gasoline dispensed in the United States and internationally.