Naming Alkanes

Naming of Saturated Hydrocarbons:

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Naming of Saturated Hydrocarbons.


Naming of Saturated Unbranched Chain Compounds and Radicals 

Names of the  members of this series consist of a numerical term, followed by "-ane" with elision of terminal "a" from the numerical term. The generic name of saturated acyclic hydrocarbons (branched or unbranched) is "alkane".

Examples of names:

1   Methane

22 Docosane

2   Ethane

23 Tricosane

3   Propane

24 Tetracosane

4   Butane

25 Pentacosane

5   Pentane

26 Hexacosane

6   Hexane

27 Heptacosane

7   Heptane

28 Octacosane

8   Octane

29 Nonacosane

9   Nonane

30 Triacontane

10 Decane

31 Hentriacontane

11 Undecane

32 Dotriacontane

12 Dodecane

33 Tritriacontane

13 Tridecane

40 Tetracontane

14 Tetradecane

50 Pentacontane

15 Pentadecane

60 Hexacontane

16 Hexadecane

70 Heptacontane

17 Heptadecane

80 Octacontane

18 Octadecane

90 Nonacontane

19 Nonadecane

100 Hectane

20 Icosane 

132 Dotriacontahectane

21 Henicosane


Naming Radicals: Univalent radicals derived from saturated unbranched acyclic hydrocarbons by removal of hydrogen from a terminal carbon atom are named by replacing the ending "-ane" of the name of the hydrocarbon by "-yl".

The carbon atom with the free valence is numbered as 1. As a class, these radicals are  alkyls.

A saturated branched acyclic hydrocarbon is named by prefixing the designations of the side chains to the name of the longest chain present in the formula.


The following names are retained for unsubstituted hydrocarbons only:

Isobutane       ,Isopentane     ,Neopentane   ,Isohexane      

LOWEST LOCANT RULE : The longest chain is numbered from one end to the other by Arabic numerals, the direction being so chosen as to give the lowest numbers possible to the side chains. When series of locants containing the same number of terms are compared term by term, that series is "lowest" which contains the lowest number on the occasion of the first difference. This principle is applied irrespective of the nature of the substituent’s.

NAMING BRANCHED CHAIN: Univalent branched radicals derived from alkanes are named by prefixing the designation of the side chains to the name of the unbranched alkyl radical possessing the longest possible chain starting from the carbon atom with the free valence, the said atom being numbered as 1.




The following names may be used for the unsubstituted radicals only:

Isopropyl, Isobutyl, sec-Butyl , tert-Butyl , Isopentyl ,Neopentyl ,tert-Pentyl , Isohexyl.

Alphabetical oder : If two or more side chains of different nature are present, they are cited in alphabetical order.

The alphabetical order is decided as follows:

(i) The names of simple radicals are first alphabetized and the multiplying prefixes are then multiplying prefixes are not considered in alphabetization.

4-Ethyl-3,3-dimethylheptane [di ignored in alphabetization]

(ii) The name of a complex radical is considered to begin with the first letter of its complete name.


A complex radical: Radical which has digits and numeral prefix in itslf. Such radicals are written in parenthesis.

Digits : In cases where names of complex radicals are composed of identical words, priority for citation is given to that radical which contains the lowest locants at the first cited point of difference in the radical.

If two or more side chains are in equivalent positions, the one to be assigned the lower number is that cited first in the name.

Multiplying prefix  for simple radicals: The presence of identical unsubstituted radicals is indicated by the appropriate multiplying prefix di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-, undeca, etc.

Multiplying prefix  for complex radicals:  The presence of identical radicals each substituted in the same way may be indicated by the appropriate multiplying prefix bis-, tris-, tetrakis-, pentakis-, etc. The complete expression denoting such a side chain may be enclosed in parentheses .




Maximum Substituent :  If chains of equal length are competing for selection as main chain in a saturated branched acyclic hydrocarbon, then the choice goes in series to:

(a) The chain which has the greatest number of side chains.

(b) The chain whose side chains have the lowest-numbered locants.

(c) The chain having the greatest number of carbon atoms in the smaller side chains.

(d) The chain having the least branched side chains.