IUPAC nomenclature of alkanes

IUPAC = International Union of Pure and Applied Chemistry. Rules:

1. Choose the longest continuous chain of carbon atoms (straight or bent). Its alkane name is the parent name.
2. Number the carbons of that chain starting from the end nearer to the first branch, so the branches get the lowest possible numbers. (If the chain has no branch, number from either end.)
3. Name = position number(s) – branch name(s) + parent. Example: CH₃–CH(CH₃)–CH₂–CH₂–CH₃ = 2-methylpentane; CH₃CH₂CH(CH₃)CH₂CH₂CH₃ = 3-methylhexane.
4. If a branch is repeated, use di-, tri-, tetra- and give a number for each: 2,3-dimethylpentane; 3,3-dimethylpentane.
5. Substituents such as Cl, Br, NO₂ are named chloro, bromo, nitro (ending with o): CH₃–CHBr–CH₃ = 2-bromopropane; CH₃–CCl₂–CH₂–CH₃ = 2,2-dichlorobutane.
6. If different groups are present, list them alphabetically (ignoring di-, tri-), after numbering so that the sum of the numbers is lowest: e.g. 2-bromo-3-methylbutane; 3-chloro-4,4-dimethylhexane.
7. Numbers are separated by commas; numbers are separated from words by hyphens.

More examples: (CH₃)₃C–CH₂–CH₃ = 2,2-dimethylbutane; CH₃–CH(CH₃)–CH(CH₃)–CH₂CH₃ = 2,3-dimethylpentane; a nonane chain with ethyl at C4 and methyls at C2 and C7 = 4-ethyl-2,7-dimethyloctane (the longest chain must be octane in that case).