IUPAC nomenclature of organic chemistry


In chemical nomenclature, the IUPAC nomenclature of organic chemistry is a method of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry. It is published in the Nomenclature of Organic Chemistry. Ideally, every possible organic compound should have a name from which an unambiguous structural formula can be created. There is also an IUPAC nomenclature of inorganic chemistry.
To avoid long and tedious names in normal communication, the official IUPAC naming recommendations are not always followed in practice, except when it is necessary to give an unambiguous and absolute definition to a compound. IUPAC names can sometimes be simpler than older names, as with ethanol, instead of ethyl alcohol. For relatively simple molecules they can be more easily understood than non-systematic names, which must be learnt or looked over. However, the common or trivial name is often substantially shorter and clearer, and so preferred. These non-systematic names are often derived from an original source of the compound. In addition, very long names may be less clear than structural formula.

Basic principles

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 for naming an organic compound are:
  1. Identification of the parent hydrocarbon chain. This chain must obey the following rules, in order of precedence:
  2. #It should have the maximum length.
  3. # It should have the maximum number of substituents of the suffix functional group. By suffix, it is meant that the parent functional group should have a suffix, unlike halogen substituents. If more than one functional group is present, the one with [|highest precedence] should be used.
  4. # It should have the maximum number of multiple bonds.
  5. # It should have the maximum number of single bonds.
  6. Identification of the parent functional group, if any, with the highest order of precedence.
  7. Identification of the side-chains. Side chains are the carbon chains that are not in the parent chain, but are branched off from it.
  8. Identification of the remaining functional groups, if any, and naming them by their ionic prefixes.
    Different side-chains and functional groups will be grouped together in alphabetical order.. When both side chains and secondary functional groups are present, they should be written mixed together in one group rather than in two separate groups.
  9. Identification of double/triple bonds.
  10. Numbering of the chain. This is done by first numbering the chain in both directions, and then choosing the numbering which follows these rules, in order of precedence
  11. # Has the lowest-numbered locant for the suffix functional group. Locants are the numbers on the carbons to which the substituent is directly attached.
  12. # Has the lowest-numbered locants for multiple bonds.
  13. # Has the lowest-numbered locants for prefixes.
  14. Numbering of the various substituents and bonds with their locants. If there is more than one of the same type of substituent/double bond, a prefix is added showing how many there are
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-. If there are both double bonds and triple bonds, "en" is written before "yne". When the main functional group is a terminal functional group, there is no need to number it.
  1. Arrangement in this form: Group of side chains and secondary functional groups with numbers made in step 3 + prefix of parent hydrocarbon chain + double/triple bonds with numbers + primary functional group suffix with numbers.
Wherever it says "with numbers", it is understood that between the word and the numbers, the prefix is used.
  1. Adding of punctuation:
  2. # Commas are put between numbers
  3. # Hyphens are put between a number and a letter
  4. # Successive words are merged into one word
    Note: IUPAC uses one-word names throughout. This is why all parts are connected.
The finalized name should look like this:

#,#-di<side chain>-#-<secondary functional group>-#-<side chain>-#,#,#-tri<secondary functional group><parent chain prefix><If all bonds are single bonds, use "ane">-#,#-di<double bonds>-#-<triple bonds>-#-<primary functional group>

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.
; Example
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, following the above steps:
  1. The parent hydrocarbon chain has 23 carbons. It is called tricosa-.
  2. The functional groups with the highest precedence are the two ketone groups.
  3. # The groups are on carbon atoms 3 and 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 are numbered 3 and 9. When numbering from right to left, the ketone groups are numbered 15 and 21. 3 is less than 15, therefore the ketones are numbered 3 and 9. The smaller 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.
  6. * There are two ethyl- groups. They are combined to create, 4,8-diethyl.
  7. * The side chains are grouped like this: 12-butyl-4,8-diethyl.
  8. 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, this gives 18-bromo-12-butyl-11-chloro-4,8-diethyl-5-hydroxy-15-methoxy.
  9. There are two double bonds: one between carbons 6 and 7, and one between carbons 13 and 14. They would be called "6,13-diene", but the presence of alkynes switches it to 6,13-dien. There is one triple bond between carbon atoms 19 and 20. It will be called 19-yne.
  10. The arrangement is: 18-bromo-12-butyl-11-chloro-4,8-diethyl-5-hydroxy-15-methoxytricosa-6,13-dien-19-yne-3,9-dione
  11. Finally, due to cis-trans isomerism, we have to specify the relative orientation of functional groups around each double bond. For this example, we have
The final name is -18-bromo-12-butyl-11-chloro-4,8-diethyl-5-hydroxy-15-methoxytricosa-6,13-dien-19-yne-3,9-dione.

Hydrocarbons

Alkanes

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:
Number of carbons1234567891011121314151617181920
PrefixMethEthPropButPentHexHeptOctNonDecUndecDodecTridecTetradecPentadecHexadecHeptadecOctadecNonadecIcos

For example, the simplest alkane is CH4 methane, and the nine-carbon alkane CH37CH3 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 cyclohexane.

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, 2CHCH3, commonly known as isobutane, is treated as a propane chain with a methyl group bonded to the middle 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 possibly occur on any of the other carbon atoms and therefore the use of the number "2" is unnecessary.
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 smaller number is used. For example, 2CHCH2CH3 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. For example, C4 is named 2,2-dimethylpropane. If there are different groups, they are added in alphabetical order, separated by commas or hyphens:. 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.

Alkenes

Alkenes are named for their parent alkane chain with the suffix "-ene" and an infixed number indicating the position of the carbon with the lower number for each double bond 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 may be indicated with a prefixed cis- or trans-: cis-but-2-ene, trans-but-2-ene. However, cis- and trans- are relative descriptors. It is IUPAC convention to describe all alkenes using absolute descriptors of Z- and E- with the Cahn–Ingold–Prelog priority rules.

Alkynes

Alkynes are named using the same system, with the suffix "-yne" indicating a triple bond: ethyne, propyne.

Functional groups

Haloalkanes and Haloarenes

In Haloalkanes and Haloarenes, Halogen functional groups are prefixed with the bonding position and take the form of fluoro-, chloro-, bromo-, iodo-, etc., depending on the halogen. Multiple groups are dichloro-, trichloro-, etc., and dissimilar groups are ordered alphabetically as before. For example, CHCl3 is trichloromethane. The anesthetic Halothane is 2-bromo-2-chloro-1,1,1-trifluoroethane.

Alcohols

Alcohols take the suffix "-ol" with an infix numerical bonding position: CH3CH2CH2OH is propan-1-ol. The suffixes,,, etc., are used for multiple -OH groups: Ethylene glycol CH2OHCH2OH is ethane-1,2-diol.
If higher precedence functional groups are present, the prefix "hydroxy" is used with the bonding position: CH3CHOHCOOH is 2-hydroxypropanoic acid.

Ethers

Ethers consist of an oxygen atom between the two attached carbon chains. The shorter of the two chains becomes the first part of the name with the -ane suffix changed to -oxy, and the longer alkane chain becomes the suffix of the name of the ether. Thus, CH3OCH3 is methoxymethane, and CH3OCH2CH3 is methoxyethane. If the oxygen is not attached to the end of the main alkane chain, then the whole shorter alkyl-plus-ether group is treated as a side-chain and prefixed with its bonding position on the main chain. Thus CH3OCH2 is 2-methoxypropane.
Alternatively, an ether chain can be named as an alkane in which one carbon is replaced by an oxygen, a replacement denoted by the prefix "oxa". For example, CH3OCH2CH3 could also be called 2-oxabutane, and an epoxide could be called oxacyclopropane. This method is especially useful when both groups attached to the oxygen atom are complex.

Aldehydes

Aldehydes take the suffix "-al". If other functional groups are present, the chain is numbered such that the aldehyde carbon is in the "1" position, unless functional groups of higher precedence are present.
If a prefix form is required, "oxo-" is used, with the position number indicating the end of a chain: CHOCH2COOH is 3-oxopropanoic acid. If the carbon in the carbonyl group cannot be included in the attached chain, the prefix "formyl-" or the suffix "-carbaldehyde" is used: C6H11CHO is cyclohexanecarbaldehyde. If an aldehyde is attached to a benzene and is the main functional group, the suffix becomes benzaldehyde.

Ketones

In general ketones take the suffix "-one" with an infix position number: CH3CH2CH2COCH3 is pentan-2-one. If a higher precedence suffix is in use, the prefix "oxo-" is used: CH3CH2CH2COCH2CHO is 3-oxohexanal.

Carboxylic acids

In general, carboxylic acids are named with the suffix -oic acid. As with aldehydes, the carboxyl functional group must take the "1" position on the main chain and so the locant need not be stated. For example, CH3-CH-COOH is named 2-hydroxypropanoic acid with no "1" stated. Some traditional names for common carboxylic acids are in such widespread use that they are retained in IUPAC nomenclature, though systematic names like ethanoic acid are also used. Carboxylic acids attached to a benzene ring are structural analogs of benzoic acid and are named as one of its derivatives.
If there are multiple carboxyl groups on the same parent chain, multiplying prefixes are used: Malonic acid,, is systematically named propanedioic acid. Alternatively, the suffix can be used, combined with a multiplying prefix if necessary - mellitic acid is benzenehexacarboxylic acid, for example. In the latter case, the carbon atom in the carboxyl group do not count as being part of the main chain, a rule that also applies to the prefix form "carboxy-". Citric acid serves as an example: it is formally named rather than.

Carboxylates

of carboxylic acids are named following the usual cation-then-anion conventions used for ionic compounds in both IUPAC and common nomenclature systems. The name of the carboxylate anion is derived from that of the parent acid by replacing the "–oic acid" ending with "–oate." For example,, the sodium salt of benzoic acid, is called sodium benzoate. Where an acid has both a systematic and a common name, its salts can be named from either parent name. Thus, can be named as potassium acetate or as potassium ethanoate.

Esters

Esters are named as alkyl derivatives of carboxylic acids. The alkyl group is named first. The R-CO-O part is then named as a separate word based on the carboxylic acid name, with the ending changed from -oic acid to -oate. For example, CH3CH2CH2CH2COOCH3 is methyl pentanoate, and 2CHCH2CH2COOCH2CH3 is ethyl 4-methylpentanoate. For esters such as ethyl acetate, ethyl formate or dimethyl phthalate that are based on common acids, IUPAC recommends use of these established names, called . The -oate changes to -ate. Some simple examples, named both ways, are shown in the figure above.
If the alkyl group is not attached at the end of the chain, the bond position to the ester group is infixed before "-yl": CH3CH2CHOOCCH2CH3 may be called but-2-yl propanoate or but-2-yl propionate.

Acyl Groups

Acyl groups are named by stripping the -ic acid of the corresponding carboxylic acid and replacing it with -yl. For Example, CH3CO-R is called Ethanoyl-R.

Acyl Halides

Simply add the name of the attached halide to the end of the acyl group. For example, CH3COCl is Ethanoyl Chloride.

Acid Anhydrides

If both acyl groups are the same, then the name of the carboxylic acid with the word acid replaced with anhydride and IUPAC name consists of two words. If the acyl groups are different, then they are named in alphabetical order in the same way, with anhydride replacing acid and IUPAC name consists of three words. For example, CH3CO-O-OCCH3 is called Ethanoic Anhydride,
CH3CO-O-OCCH2CH3 is called Ethanoic Propanoic Anhydride.

Amines

Amines are named for the attached alkane chain with the suffix "-amine". If necessary, the bonding position is infixed: CH3CH2CH2NH2 propan-1-amine, CH3CHNH2CH3 propan-2-amine. The prefix form is "amino-".
For secondary amines, the longest carbon chain attached to the nitrogen atom becomes the primary name of the amine; the other chain is prefixed as an alkyl group with location prefix given as an italic N: CH3NHCH2CH3 is N-methylethanamine. Tertiary amines are treated similarly: CH3CH2NCH2CH2CH3 is N-ethyl-N-methylpropanamine. Again, the substituent groups are ordered alphabetically.

Amides

Amides take the suffix "-amide", or "-carboxamide" if the carbon in the amide group cannot be included in the main chain. The prefix form is both "carbamoyl-" and "amido-".e.g HCONH2 Methanamide,CH3CONH2 Ethanamide.
Amides that have additional substituents on the nitrogen are treated similarly to the case of amines: they are ordered alphabetically with the location prefix N: HCON2 is N,N-dimethylmethanamide,CH3CON2 is N,N-dimethyethanamide.

Nitriles

Nitriles are named by adding the suffix -nitrile to the longest hydrocarbon chain. It can also be named by replacing the -oic acid of their corresponding carboxylic acids with -onitrile. Functional class IUPAC nomenclature may also be used in the form of alkyl cyanides. For example, CH3CH2CH2CH2CN is called pentanenitrile or butyl cyanide.

Cyclic compounds

s and aromatic compounds can be treated as the main parent chain of the compound, in which case the positions of substituents are numbered around the ring structure. For example, the three isomers of xylene CH3C6H4CH3, commonly the ortho-, meta-, and para- forms, are 1,2-dimethylbenzene, 1,3-dimethylbenzene, and 1,4-dimethylbenzene. The cyclic structures can also be treated as functional groups themselves, in which case they take the prefix "cycloalkyl-" or for benzene, "phenyl-".
The IUPAC nomenclature scheme becomes rapidly more elaborate for more complex cyclic structures, with notation for compounds containing conjoined rings, and many common names such as phenol being accepted as base names for compounds derived from them.

Order of precedence of groups

When compounds contain more than one functional group, the order of precedence determines which groups are named with prefix or suffix forms. The table below shows common groups in decreasing order of precedence. The highest-precedence group takes the suffix, with all others taking the prefix form. However, double and triple bonds only take suffix form and are used with other suffixes.
Prefixed substituents are ordered alphabetically, e.g. chlorofluoromethane, not fluorochloromethane. If there are multiple functional groups of the same type, either prefixed or suffixed, the position numbers are ordered numerically The N position indicator for amines and amides comes before "1", e.g. CH3CHCH2NH is N,2-dimethylpropanamine.
PriorityFunctional groupFormulaPrefixSuffix
1Cations
e.g. Ammonium
NH4+		-onio-
ammonio-		-onium
-ammonium
2Carboxylic acids
  • Note: These suffixes, in which the carbon atom is counted as part of the preceding chain, are the most commonly used. See individual functional group articles for more details.
The order of remaining functional groups is only needed for substituted benzene and hence is not mentioned here.

Common nomenclature – trivial names

Common nomenclature uses the older names for some organic compounds instead of using the prefixes for the carbon skeleton above. The pattern can be seen below.
Number of
carbons		Prefix as in
new system		Common name
for alcohol		Common name
for aldehyde		Common name
for acid		Common name
for ketone
1Meth-Methyl alcohol
FormaldehydeFormic acidNA
2Eth-Ethyl alcohol
AcetaldehydeAcetic acidNA
3Prop-Propyl alcoholPropionaldehydePropionic acidAcetone/dimethyl ketone
4But-Butyl alcoholButyraldehydeButyric acidEthyl methyl ketone
5Pent-Amyl alcoholValeraldehydeValeric acid•Methyl propyl ketone
•Diethyl ketone
6Hex-Caproyl alcoholCaproaldehydeCaproic acid•Butyl methyl ketone
•Ethyl propyl ketone
7Hept-Enanthyl alcoholEnanthaldehydeEnanthoic acid•Methyl pentyl ketone
•Butyl Ethyl ketone
•Dipropyl ketone
8Oct-Capryl alcoholCaprylaldehydeCaprylic acid•Hexyl methyl ketone
•Ethyl pentyl ketone
•Butyl propyl ketone
9Non-Pelargonic alcoholPelargonaldehydePelargonic acid•Heptyl methyl ketone
•Ethyl hexyl ketone
•Pentyl propyl ketone
•Dibutyl ketone
10Dec-Capric alcoholCapraldehydeCapric acid•Methyl octyl ketone
•Ethyl heptyl ketone
•Hexyl propyl ketone
•Butyl pentyl ketone
11Undec----The same pattern continues
'
12Dodec-Lauryl alcoholLauraldehydeLauric acidThe same pattern continues
'
13Tridec----The same pattern continues
'
14Tetradec-Myristyl alcoholMyristaldehydeMyristic acidThe same pattern continues
'
15Pentadec----The same pattern continues
'
16Hexadec-Cetyl alcohol
Palmityl alcohol		PalmitaldehydePalmitic acidThe same pattern continues
'
17Heptadec---Margaric acidThe same pattern continues
'
18Octadec-Stearyl alcoholStearaldehydeStearic acidThe same pattern continues
'
19Nonadec----The same pattern continues
'
20Icos-Arachidyl alcohol-Arachidic acidThe same pattern continues
'
21Henicos----The same pattern continues
'
22Docos-Behenyl alcohol-Behenic acidThe same pattern continues
'
23Tricos----The same pattern continues
'
24Tetracos-Lignoceryl alcohol-Lignoceric acidThe same pattern continues
'
25Pentacos----The same pattern continues
'
26Hexacos-Ceryl alcohol-Cerotic acidThe same pattern continues
'
27Heptacos----The same pattern continues
'
28Octacos-Montanyl alcohol-Montanic acidThe same pattern continues
'
29Nonacos----The same pattern continues
'
30Triacont-Melissyl alcohol-Melissic acidThe same pattern continues
'
31Hentriacont----The same pattern continues
'
32Dotriacont-Lacceryl alcohol-Lacceroic acidThe same pattern continues
'
33Tritriacont-Psyllic alcohol-Psyllic acidThe same pattern continues
'
34Tetratriacont-Geddyl alcohol-Geddic acidThe same pattern continues
'
35Pentatriacont---Ceroplastic acidThe same pattern continues
'
36Hexatriacont----The same pattern continues
'
37Heptatriacont----The same pattern continues
'
38Octatriacont----The same pattern continues
'
39Nonatriacont----The same pattern continues
'
40Tetracont----The same pattern continues
'

Ketones

Common names for ketones can be derived by naming the two alkyl or aryl groups bonded to the carbonyl group as separate words followed by the word ketone.
  • Acetone
  • Acetophenone
  • Benzophenone
  • Ethyl isopropyl ketone
  • Diethyl ketone
The first three of the names shown above are still considered to be .

Aldehydes

The common name for an aldehyde is derived from the common name of the corresponding carboxylic acid by dropping the word acid and changing the suffix from -ic or -oic to -aldehyde.
  • Formaldehyde
  • Acetaldehyde

    Ions

The IUPAC nomenclature also provides rules for naming ions.

Hydron

is a generic term for hydrogen cation; protons, deuterons and tritons are all hydrons.
The Hydrons are not found in heavier isotopes, however.

Parent hydride cations

Simple cations formed by adding a hydron to a hydride of a halogen, chalcogen or pnictogen are named by adding the suffix "-onium" to the element's root: H4N+ is ammonium, H3O+ is oxonium, and H2F+ is fluoronium. Ammonium was adopted instead of nitronium, which commonly refers to NO2+.
If the cationic center of the hydride is not a halogen, chalcogen or pnictogen then the suffix "-ium" is added to the name of the neutral hydride after dropping any final 'e'. H5C+ is methanium, HO--H2 is dioxidanium, and H2N--H3 is diazanium.

Cations and substitution

The above cations except for methanium are not, strictly speaking, organic, since they do not contain carbon. However, many organic cations are obtained by substituting another element or some functional group for a hydrogen.
The name of each substitution is prefixed to the hydride cation name. If many substitutions by the same functional group occur, then the number is indicated by prefixing with "di-", "tri-" as with halogenation. 3O+ is trimethyloxonium. CH3F3N+ is trifluoromethylammonium.
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