The third homologous series is the cycloalkanes. Their names all end in –ane and begin with cyclo-, for example cyclopropane. The cycloalkanes have the general formula .
Even though they have the same general formula as the alkenes, the cycloalkanes are saturated and contain only single bonds. This means that they do not quickly decolourise bromine solution. Cyloalkanes are isomers of the alkenes.
Many cycloalkanes are used in motor fuel, natural gas, kerosene, diesel and other heavy oils.