Isobutane, neopentane, etc. are trivial names that arise from common usage. As you can see, the number of isomers increases rapidly for larger alkanes. It would be impractical to give trivial names to every isomer. What is needed is a systematic, easy-to-use method of naming that works for even the most complex of molecules. Such a name should unambiguously identify the structural formula of the named molecule. This system is IUPAC nomenclature, devised by the International Union of Pure and Applied Chemists.

The IUPAC system considers molecules in terms of a parenthydrocarbon chain with substituents attached to it. The parent is the longest continuous carbon chain in the compound, and the base name of the compound is the alkane that corresponds to the parent chain. Then, consecutively number the carbons of the parent chain in such a way that the substituents are attached to carbons withlower numbers. The name of the compound is the parent alkane prefixed by its substituents and their position numberings.

In n-alkanes, no carbon is bonded to more than two other carbons, giving rise to a linear chain. When a carbon is bonded to more than two other carbons, a branch is formed. The smallest branched alkane is isobutane. Notice that isobutane has the same molecular formula, C 4 H 10 , as n-butane but has a different structural formula. Two different molecules which have the same molecular formula are isomers. Isomers which differ in the connectivity of bonds are constitutional isomers, or structural isomers. Isobutane is a constitutional isomer of n-butane. The prefix "iso" indicates that branches off of the central carbon are equivalent.n-butane and isobutane are the only constitutional isomers of C 4 H 10 . Pentane, C 5 H 12 , has three while hexane, C 6 H14 , has five.