Systematic nomenclature and isomerism of alkanes

Systematic nomenclature rests on the 1892 Geneva rules, later refined by IUPAC (International Union of Pure and Applied Chemistry). First choose the longest chain, preferring the most branched one, as the main chain. Number it from the end nearer the substituents; if both ends are equally near, start from the side that gives the lower set of numbers. The name lists the substituents with their numbers in alphabetical order, uses di-, tri-, tetra- for identical radicals and ends with the main-chain name, e.g. 3-ethyl-2-methylhexane. Halogens are named as substituents too: 2-bromo-3-methylbutane. A carbon is primary (1 carbon neighbour), secondary (2), tertiary (3) or quaternary (4) according to the number of carbon atoms bonded to it. The number of isomers grows quickly with carbon number: pentane 3, hexane 5, heptane 9, decane 75.