IUPAC NOMENCLATURE OF ORGANIC CHEMISTRY
The IUPAC nomenclature of organic chemistry is a systematic method of naming organic chemical
compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC).
Ideally, every organic compound should have a name from which an unambiguous structural formula
can be drawn. There is also an IUPAC nomenclature of inorganic chemistry.
The main idea of IUPAC nomenclature is that every compound has one and only one name, and every
name corresponds to only one structure of molecules (i.e. a one-one relationship), thereby reducing
For ordinary communication, to spare a tedious description, the official IUPAC naming recommendations
are not always followed in practice except when it is necessary to give a concise definition to a
compound, or when the IUPAC name is simpler (viz. ethanol against ethyl alcohol). Otherwise the
common or trivial name may be used, often derived from the source of the compound
In chemistry, a number of prefixes, suffixes and infixes are used to describe the type and position of
functional groups in the compound.
The steps to naming an organic compound are:
1. Identify the parent hydrocarbon chain (The longest continuous chain of carbon atoms)
2. Identify the functional group, if any (If more than one, use the one with highest precedence
3. Identify the position of the functional group in the chain.
4. Number the carbon atoms in the parent chain. The functional group should end up the least number
possible (as there are two ways of numbering --right to left and left to right). The number (in Arabic
numerals, i.e. 1, 2, 3....) is written before the name of the functional group suffix (such as -ol, -one, -
al, etc.). If the group is a group that can only exist at the end of any given chain (such as the
carboxylic acid and aldehyde groups), it need not be numbered.
Note: If there are no functional groups, number in both directions, find the numbers of the side-chains
(the carbon chains that are not in the parent chain) in both directions. The end result should be such
that the first number should be the least possible. In the event of the first numbers being the same for
two methods of numbering, the sum of the numbers of the side chains should be made the least
possible; for example, 2,2,5-trimethylhexane (2 + 2 + 5 = 9) is preferred over 2,5,5-trimethylhexane
(2 + 5 + 5 = 12), as they both start with '2', but the sum of the numbers of the former is less.
5. Identify the side-chains and number them. Side chains are the carbon chains that are not in the
parent chain, but are branched off from it.
If there is more than one of the same type of side-chain, add the prefix (di-, tri-, etc.) before it. The
numbers for that type of side chain will be grouped in ascending order and written before the name of
the side-chain. If there are two side-chains with the same alpha carbon, the number will be written
twice. Example: 2,2,3-trimethyl...
6. Identify the remaining functional groups, if any, and name them by the name of their ions (such as
hydroxy for -OH, oxy for =O, oxyalkane for O-R, etc.).
Different side-chains and functional groups will be grouped together in alphabetical order. (The
prefixes di-, tri-, etc. are not taken into consideration for grouping alphabetically. For example, ethyl
comes before dihydroxy or dimethyl, as the "e" in "ethyl" precedes the "h" in "dihydroxy" and the "m"
in "dimethyl" alphabetically. The "di" is not considered in either case). In the case of there being both
side chains and secondary functional groups, they should be written mixed together in one group rather
than in two separate groups.
7. Identify double/triple bonds. Number them with the number of the carbon atom at the head of the
bond (i.e. the carbon atom with the lesser number that it is attached to). For example a double bond
between carbon atoms 3 and 4 is numbered as 3-ene. Multiple bonds of one type (double/triple) are
named with a prefix (di-, tri-, etc.). If both types of bonds exist, then use "ene" before "yne" e.g. "6 13
diene 19 yne". If all bonds are single, use "ane" without any numbers or prefixes.
8. Arrange everything like this: Group of side chains and secondary functional groups with
numbers made in step 3 + prefix of parent hydrocarbon chain (eth, meth) + double/triple
bonds with numbers (or "ane") + primary functional group suffix with numbers.
Wherever it says "with numbers", it is understood that between the word and the numbers,
you use the prefix(di-, tri-)
1. Add punctuation:
2. Put commas between numbers (2 5 5 becomes 2,5,5)
3. Put a hyphen between a number and a letter (2 5 5 trimethylhexane becomes 2,5,5-
4. Successive words are merged into one word (trimethyl hexane becomes trimethylhexane)
NOTE: IUPAC uses one-word names throughout. This is why all parts are connected.
The finalized name should look like this:
Note: # is used for a number. The group secondary functional groups and side chains may not look the
same as shown here, as the side chains and secondary functional groups are arranged alphabetically.
The di- and tri- have been used just to show their usage. (di- after #,#, tri- after #,#,# , etc.)
Here is a sample molecule with the parent carbons numbered:
For simplicity, here is an image of the same molecule, where the hydrogens in the parent chain are
removed and the carbons are shown by their numbers:
Now, we go by the steps:
1. The parent hydrocarbon chain has 23 carbons. It is called tricos-.
2. The functional groups with the highest precedence are the two ketone groups.
3. The groups are on carbon atoms 3 & 9. As there are two, we write 3,9-dione.
4. The numbering of the molecule is based on the ketone groups. when numbering from left to
right, the ketone groups get numbered 3 and 9.when numbering from right to left, the ketone
groups get numbered 15 and 21. 3 is less than 15, therefore, the numbering is done left to
right, and the ketones are numbered 3 & 9. The lesser number is always used, not the sum of
the constituents numbers.
5. The side chains are: an ethyl- at carbon 4, an ethyl- at carbon 8, and a butyl- at carbon 12.
NOTE: The -O-CH3 at carbon atom 15 is not a side chain, but it is a methoxy functional group
o There are two ethyl- groups, so they are combined to create, 4,8-diethyl.
o The side chains shall be grouped like this: 12-butyl-4,8-diethyl. (But this is not the final
grouping, as functional groups may be added in between.)
The secondary functional groups are: a hydroxy- at carbon 5, a chloro- at carbon 11, a methoxy- at
carbon 15, and a bromo- at carbon 18. Grouped with the side chains, we get 18-bromo-12-butyl-11-
There are two double bonds: one between carbons 6 & 7, and one between carbons 13 & 14. They will
be called 6,13-diene. There is one triple bond between carbon atoms 19 & 20. It will be called 19-yne
The arrangement (with punctuation) is: 18-bromo-12-butyl-11-chloro-4,8-diethyl-5-hydroxy-15-
The final name is 18-bromo-12-butyl-11-chloro-4,8-diethyl-5-hydroxy-15-methoxytricos-6,13-
Straight-chain alkanes take the suffix "-ane" and are prefixed depending on the number of carbon
atoms in the chain, following standard rules. The first few are:
1 2 3 4 5 6 7 8 9 10 11 12 13
Prefix Meth Eth Prop But Pent Hex Hept Oct Non Dec Undec Dodec Tridec
For example, the simplest alkane is CH 4 methane, and the nine-carbon alkane CH3(CH2)7CH3 is named
nonane. The names of the first four alkanes were derived from methanol, ether, propionic acid and
butyric acid, respectively. The rest are named with a Greek numeric prefix, with the exceptions of
nonane which has a Latin prefix, and undecane and tridecane which have mixed-language prefixes.
Cyclic alkanes are simply prefixed with "cyclo-", for example C4H8 is cyclobutane and C6H12 is
Branched alkanes are named as a straight-chain alkane with attached alkyl groups. They are prefixed
with a number indicating the carbon the group is attached to, counting from the end of the alkane
chain. For example, (CH3)2CHCH3, commonly known as isobutane, is treated as a propane chain with a
methyl group bonded to the middle (2) carbon, and given the systematic name 2-methylpropane.
However, although the name 2-methylpropane COULD be used, it is easier and more logical to call it
simply methylpropane - the methyl group could not possible occur on any of the other cabon atoms
(that would lengthen the chain and result in butane, not propane) and therefore the use of the number
"2" is not necessary.
If there is ambiguity in the position of the substituent,
depending on which end of the alkane chain is counted as "1",
then numbering is chosen so that the smallest number is used.
For example, (CH3)2CHCH2CH3 (isopentane) is named 2-
methylbutane, not 3-methylbutane.
If there are multiple side-branches of the same size alkyl group, their positions are separated by
commas and the group prefixed with di-, tri-, tetra-, etc., depending on the number of branches (e.g.
C(CH3)4 2,2-dimethylpropane). If there are different groups, they are added in alphabetical order,
separated by commas or hyphens: 3-ethyl-4-methylhexane. The longest possible main alkane chain is
used; therefore 3-ethyl-4-methylhexane instead of 2,3-diethylpentane, even though these describe
equivalent structures. The di-, tri- etc. prefixes are ignored for the purpose of alphabetical ordering of
side chains (e.g. 3-ethyl-2,4-dimethylpentane, not 2,4-dimethyl-3-ethylpentane).
Alkenes and Alkynes
Alkenes are named for their parent alkane chain with the
suffix "-ene" and an infixed number indicating the position of
the double-bonded carbon in the chain: CH2=CHCH2CH3 is but-
1-ene. Multiple double bonds take the form -diene, -triene,
etc., with the size prefix of the chain taking an extra "a":
CH2=CHCH=CH2 is buta-1,3-diene. Simple cis and trans
isomers are indicated with a prefixed cis- or trans-: cis-but-2-
More complex geometric isomerisations are described using the Cahn Ingold Prelog priority rules.
Alkynes are named using the same system, with the suffix "-yne" indicating a triple bond: ethyne
Alk is the prefix of the group (Meth, Eth, Prop, etc.)
IUPAC nomenclature for cyclic
IUPAC parent chains Common
nomenclature (if different from straight nomenclature
R-- Alkyl - Alkyl
Halogens Halo'alkane - Alkyl halide
Alcohols R--OH Alkanol - Alkyl alcohol
Amines R--NH2 Alkanamine - Alkyl amine
Carboxylic (Alk + 1)anoic
Cycloalkanecarboxylic acid -
Aldehydes Alkanal Cycloalkanecarboxaldehyde -
Ketones Alkanone -
Thiols R--SH Alkanethiol - -
Amides Cycloalkanecarboxamide -
Ethers R1--O--R2 alkoxyalkane -
Alk(1)yl Alk(1)yl Alk(1)yl (Alk +
Alk(2)aneoate Cycloalk(2)anecarboxylate 1)(2)anoate
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