Acyclic Hydrocarbons
Rule A-1. Saturated Unbranched-chain Compounds and Univalent Radicals 
1.1 - The first four saturated unbranched acyclic hydrocarbons are called methane, ethane, propane and butane. Names of the higher members of this series consist of a numerical term, followed by "-ane" with elision of terminal "a" from the numerical term. Examples of these names are shown in the table below. The generic name of saturated acyclic hydrocarbons (branched or unbranched) is "alkane".
Examples of names:
(
n = total number of carbon atoms)
| n | n |
| 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 | |
1.2 - 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 called normal, or unbranched chain, alkyls.
Examples to Rule A-1.2
See Recommendations'93 R-2.2.1
Rule A-2. Saturated Branched-chain Compounds and Univalent Radicals
2.1 - 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.
Example to Rule A-2.1
The following names are retained for unsubstituted hydrocarbons only:
| Isobutane |  |
| Isopentane |  |
| Neopentane |  |
| Isohexane |  |
2.2 - 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 substituents.
Examples to Rule A-2.2
2.25 - 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.
Examples to Rule A-2.25
| 1-Methylpentyl |  |
| 2-Methylpentyl |  |
| 5-Methylhexyl |  |
The following names may be used for the unsubstituted radicals only:
| Isopropyl |  |
| Isobutyl |  |
| sec-Butyl |  |
| tert-Butyl |  |
| Isopentyl |  |
| Neopentyl |  |
| tert-Pentyl |  |
| Isohexyl |  |
2.3 - 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 inserted.
Examples to Rule A-2.3(i)
ethyl is cited before methyl,
thus 4-Ethyl-3,3-dimethylheptane
(ii) The name of a complex radical is considered to begin with the first letter of its complete name.
Examples to Rule A-2.3(ii)
dimethylpentyl (as complete single substituent) is alphabetized under "d",
thus 7-(1,2-Dimethylpentyl)-5-ethyltridecane
(iii) In cases where names of complex radicals are composed of identical words, priority for citation is given to that radical which contains the lowest locant at the first cited point of difference in the radical.
Examples to Rule A-2.3(iii)
2.4 - 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.
Examples: to Rule A-2.4
2.5 - The presence of identical unsubstituted radicals is indicated by the appropriate multiplying prefix di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-, undeca, etc.
Example to Rule A-2.5(a)
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 or the carbon atoms in side chains may be indicated by primed numbers.
Examples to Rule A-2.5(b)
(a) Use of parentheses and unprimed numbers:
5,5-Bis(1,1-dimethylpropyl)-2-methyldecane
(b) Use of primes:
5,5-Bis-1',1'-dimethylpropyl-2-methyldecane
(a) Use of parentheses and unprimed numbers:
7-(1,1-Dimethylbutyl)-7-(1,1-dimethylpentyl)tridecane
(b) Use of primes:
7-1',1'-Dimethylbutyl-7-1",1"-dimethylpentyltridecane
2.6 - 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.
Example to Rule A-2.6(a)
(b) The chain whose side chains have the lowest-numbered locants.
Example to Rule A-2.6(b)
(c) The chain having the greatest number of carbon atoms in the smaller side chains.
Example to Rule A-2.6(c)
(d) The chain having the least branched side chains.
Example to Rule A-2.6(d)
Rule A-3. Unsaturated Compounds and Univalent Radicals
3.1 - Unsaturated unbranched acyclic hydrocarbons having one double bond are named by replacing the ending "-ane" of the name of the corresponding saturated hydrocarbon with the ending "-ene". If there are two or more double bonds, the ending will be "-adiene", "-atriene", etc. The generic names of these hydrocarbons (branched or unbranched) are "alkene", "alkadiene", "alkatriene", etc. The chain is so numbered as to give the lowest possible numbers to the double bonds. When, in cyclic compounds or their substitution products, the locants of a double bond differ by unity, only the lower locant is cited in the name; when they differ by more than unity, one locant is placed in parentheses after the other (see Rules A-31.3 and A-31.4).
Examples to Rule A-3.1
| 2-Hexene |  |
| 1,4-Hexadiene |  |
The following non-systematic names are retained:
| Ethylene |  |
| Allene |  |
3.2 - Unsaturated unbranched acyclic hydrocarbons having one triple bond are named by replacing the ending "-ane" of the name of the corresponding saturated hydrocarbon with the ending "-yne". If there are two or more triple bonds, the ending will be "-adiyne", "atriyne", etc. The generic names of these hydrocarbons (branched or unbranched) are "alkyne", "alkadiyne", "alkatriyne", etcThe chain is so numbered as to give the lowest possible numbers to the triple bonds. Only the lower locant for a triple bond is cited in the name of a compound.
The name "acetylene" for 
is retained.
3.3 - Unsaturated unbranched acyclic hydrocarbons having both double and triple bonds are named by replacing the ending "-ane" of the name of the corresponding saturated hydrocarbon with the ending "-enyne", "-adienyne", "-atrienyne", "-enediyne", etcNumbers as low as possible are given to double and triple bonds even though this may at times give "-yne" a lower number than "-ene". When there is a choice in numbering, the double bonds are given the lowest numbers.
Examples to Rule A-3.3
| 1,3-Hexadien-5-yne |  |
| 3-Penten-1-yne |  |
| 1-Penten-4-yne |  |
3.4 - Unsaturated branched acyclic hydrocarbons are named as derivatives of the unbranched hydrocarbons which contain the maximum number of double and triple bonds. If there are two or more chains competing for selection as the chain with the maximum number of unsaturated bonds, then the choice goes to (1) that one with the greatest number of carbon atoms; (2) the number of carbon atoms being equal, that one containing the maximum number of double bonds. In other respects, the same principles apply as for naming saturated branched acyclic hydrocarbons. The chain is so numbered as to give the lowest possible numbers to double and triple bonds in accordance with Rule A-3.3.
Examples to Rule A-3.4
The following name is retained for the unsubstituted compound only:
3.5 - The names of univalent radicals derived from unsaturated acyclic hydrocarbons have the endings "-enyl", "-ynyl", "-dienyl", etc., the positions of the double and triple bonds being indicated where necessary. The carbon atom with the free valence is numbered as 1.
Examples to Rule A-3.5
| Ethynyl |  |
| 2-Propynyl |  |
| 1-Propenyl |  |
| 2-Butenyl |  |
| 1,3-Butadienyl |  |
| 2-Pentenyl |  |
| 2-Penten-4-ynyl |  |
Exceptions:The following names are retained (for unsubstituted radical only):
| Vinyl (for ethenyl) |  |
| Allyl (for 2-propenyl) |  |
| Isopropenyl(for 1-methylvinyl) |  |
3.6 - When there is a choice for the fundamental chain of a radical, that chain is selected which contains (1) the maximum number of double and triple bonds; (2) the largest number of carbon atoms; and (3) the largest number of double bonds.
Examples to Rule A-3.6
See Recommendations'93 R-3.1.1
Rule A-4. Bivalent and Multivalent Radicals
4.1 - Bivalent and trivalent radicals derived from univalent acyclic hydrocarbon radicals whose authorized names end in "-yl" by removal of one or two hydrogen atoms from the carbon atom with the free valences are named by adding "-idene" or "-idyne", respectively, to the name of the corresponding univalent radical. The carbon atom with the free valence is numbered as 1.The name "methylene" is retained for the radical 
Examples to Rule A-4.1
| Methylidyne |  |
| Ethylidene |  |
| Ethylidyne |  |
| Vinylidene |  |
| Isopropylidene |  |
4.2 - The names of bivalent radicals derived from normal alkanes by removal of a hydrogen atom from each of the two terminal carbon atoms of the chain are ethylene, trimethylene, tetramethylene, etc.
Examples to Rule A-4.2
| Pentamethylene |  |
| Hexamethylene |  |
Names of the substituted bivalent radicals are derived in accordance with Rules A-2.2 and A-2.25.
Example to Rule A-4.2a
The following name is retained:
4.3 - Bivalent radicals similarly derived from unbranched alkenes, alkadienes, alkynes, etc., by removing a hydrogen atom from each of the terminal carbon atoms are named by replacing the endings "-ene", "-diene", "-yne", etc., of the hydrocarbon name by "-enylene", "-dienylene", "-ynylene", etc., the positions of the double and triple bonds being indicated where necessary.
Example to Rule A-4.3
The following name is retained:
Names of the substituted bivalent radicals are derived in accordance with Rule A-3.4.
Example to Rule A-4.3
4.4 - Trivalent, quadrivalent and higher-valent acyclic hydrocarbon radicals of two or more carbon atoms with the free valences at each end of a chain are named by adding to the hydrocarbon name the terminations "-yl" for a single free valence, "-ylidene" for a double, and "-ylidyne" for a triple free valence on the same atom (the final "e" in the name of the hydrocarbon is elided when followed by a suffix beginning with "-yl"). If different types are present in the same radical, they are cited and numbered in the order "-yl", "-ylidene", "-ylidyne".
Examples to Rule A-4.4
| Butanediylidene |  |
| Butanediylidyne |  |
| 1-Propanyl-3-ylidene |  |
| Propadienediylidene |  |
| 2-Pentenediylidyne |  |
| 1-Butanyliden-4-ylidyne |  |
4.5 - Multivalent radicals containing three or more carbon atoms with free valences at each end of a chain and additional free valences at intermediate carbon atoms are named by adding the endings "-triyl", "-tetrayl", "-diylidene", "diyl-ylidene", etc., to the hydrocarbon name.
Examples to Rule A-4.5
See Recommendations'93 R-2.5
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