Isocetane (2,2,4,4,6,8,8-heptamethylnonane) is a highly branched alkane used as a reference in determining the cetane number of diesel. It is given a cetane number of 15. Isocetane replaced 1-methylnaphthalene as the lower reference for cetane number (1-methylnaphthalene has cetane number zero) owing to the expense of 1-methylnaphthalene, and difficulty in safe handling.