Nomenclature (AQA A Level Chemistry): Revision Note
Exam code: 7405
Nomenclature
Systematic nomenclature is used to name organic compounds, making them easier to identify and refer to
Alkanes form the basis of this naming system, and the stem of each name indicates the number of carbon atoms in the longest carbon chain of the molecule
Nomenclature of Organic Compounds Table
Number of C atoms | Molecular formula of straight-chain alkane | Name of alkane | Stem used in naming |
|---|---|---|---|
1 | CH4 | methane | meth- |
2 | C2H6 | ethane | eth- |
3 | C3H8 | propane | prop- |
4 | C4H10 | butane | but- |
5 | C5H12 | pentane | pent- |
6 | C6H14 | hexane | hex- |
Examiner Tips and Tricks
You only need to know how to name chains and rings with up to six carbon atoms each.
If side chains or functional groups are present, their positions are indicated by numbering the carbon atoms in the longest chain
Numbering starts from the end, which gives the lowest possible numbers in the name
In structural formulae, a hydrocarbon side chain is shown in brackets, for example:
CH3CH(CH3)CH2CH3
The side chain is named by adding the suffix –yl to the alkane stem. Groups of this type are called alkyl groups
If more than one identical alkyl side chain or functional group is present, the prefixes di- (two), tri- (three), or tetra- (four) are used before the group name
Commas separate adjacent numbers, while hyphens separate numbers and words
Naming Multiple Side Chains
If there is more than one type of alkyl side-chain, they are listed in alphabetical order
Examiner Tips and Tricks
An aliphatic compound is straight or branched-chain and also includes cyclic organic compounds that do not contain a benzene ring.
Functional Groups & their Nomenclature Table
Class | IUAC prefix– | Example |
|---|---|---|
alkane | –ane |  ethane |
alkene | –ene |  ethene |
halogenoalkane | fluoro– |  if X = F, fluoroethane |
alcohol | hydroxy– |  ethanol |
aldehyde | –al |  ethanal |
ketone | –one |  propanone |
carboxylic acid | –oic acid |  ethanoic acid |
ester | –oate |  methyl ethanoate |
amine | –amine |  ethylamine |
nitrile | -nitrile |  ethanenitrile |
Examiner Tips and Tricks
Ethylamine can also be called aminoethane or ethanamine. The IUPAC name is ethanamine, but past papers favour using ethylamine.
Worked Example
Naming organic molecules
Name the following molecules using correct systematic nomenclature:
Answer
The chemical name is 2,5,5-trimethylhex-2-ene
The longest carbon chain is six carbons long
There is an alkene / double carbon-carbon bond on carbon-2
There are 3 methyl groups on carbons 2, 5, and 5
The chemical name is propanal
The longest carbon chain is 3 carbons long with only single carbon-carbon bonds
There is an aldehyde group, which is fixed as carbon-1
The chemical name is 3-methylbutanal
The longest carbon chain is 4 carbons long with only single carbon-carbon bonds
There is a methyl group on carbon-3
There is an aldehyde group, which is fixed as carbon-1
The chemical name is butanoic acid
The longest carbon chain is 4 carbons long with only single carbon-carbon bonds
There is a carboxylic acid group, which is fixed as carbon-1
The chemical name is 2-chlorobutane
The longest carbon chain is 4 carbons long with only single carbon-carbon bonds
There is a chlorine atom attached to carbon-2
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