There are nine isomers of n-heptane, among which n-heptane [CH3(CH2)5CH3] is the most important. It is a colorless flammable liquid. It is almost insoluble in water, slightly soluble in alcohol, and soluble in ether and chloroform. Its vapor forms an explosive mixture with air, with an explosion limit of 1.0Chemicalbook~6.0% (volume). It is separated from petroleum fractions. It vibrates violently when it burns and explodes in the cylinder. Its octane number is set as zero. Mixtures of various proportions with *iso-octane (octane number is set as 100) are often used as standards for determining the octane number of gasoline.