are separated by fractional distillation at an oil refinery to produce petrol, jet fuel, kerosene, and other hydrocarbons. For example, 2,2,4-Trimethylpentane (isooctane), widely used in petrol , has a chemical formula of C 8 H 18 and it reacts with oxygen exothermically : [16] 2 C 8 H 18 ( l