iso-Octane is a branched hydrocarbon from the alkane group with the chemical formula C8H18. It is the most important of the eighteen octane isomers. Since it is an important component of motor gasoline, it is produced synthetically, but is also found to a small extent in petroleum.
iso-Dodecane is a branched hydrocarbon from the group of the alkanes and has a chemical formula C12H26. However, it is actually a mixture of different isomers of dodecane, usually one molecule is the main isomer, 2,2,4,6,6-pentamethylheptane. This is also the technically most important one.