Both heptane and hexane are derived from crude oil. This source means they are made from petroleum, which is why both heptane and hexane are commonly found in gasoline.


Heptane and octane scale


Heptane and hexane are both components of gasoline, but heptane has its special role in gasoline. Heptane helps determine the octane number of a fuel.


Pure heptane has an octane number of zero. The higher the octane number, the better the fuel for the car engine, because the octane number measures the fuel's ability to resist engine knock under high compression.


Engine knock refers to the combustion of the air-fuel mixture outside of the pre-ignition combustion caused by the spark plug.


Heptane is highly flammable and burns easily, which is why pure heptane fuel has a zero octane number. Gasoline companies tout "high-octane" fuels to let consumers know that their product is good for car engines, or to make people think it is.


Toxicity


Both heptane and hexane (hexane sds) are toxic, but hexane is more toxic than heptane. Both substances contain highly flammable liquids and vapors.


Other common applications


Both heptane and hexane can be used as solvents. Hexane is often used in the military and aerospace industries.