Systematic Nomenclature
- Systematic nomenclature can be used to name organic compounds and therefore make it easier to refer to them
- The alkanes provide the basis of the naming system and the stem of each name indicates how many carbon atoms are in the longest chain in one molecule of the compound
Nomenclature of Organic Compounds Table
- If there are any side-chains or functional groups present, then the position of these groups is indicated by numbering the carbon atoms in the longest chain starting at the end that gives the lowest possible numbers in the name
- The hydrocarbon side-chain is shown in brackets in the structural formula
CH3CH(CH3)CH2CH3
- The side-chain is named by adding ‘-yl’ to the normal alkane stem
- This type of group is called an alkyl group
Naming Side Chains
- If there are more than one of the same alkyl side-chain or functional groups, di- (for two), tri- (for three) or tetra- (for four) is added in front of its name
- The adjacent numbers have a comma between them
- Numbers are separated from words by a hyphen
Naming Multiple Side Chains
- If there is more than one type of alkyl side-chain, they are listed in alphabetic order
Naming Side Chains in Alphabetical Order
Examiner Tip
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
Worked example
Naming organic molecules
Name the following molecules using correct systematic nomenclature: 
Answer 1:
- 2,5,5-trimethylhex-2-ene
- The longest carbon chain is 6 carbons = hex
- There is an alkene group which is a higher priority group than the methyl side chains
- So, the carbons are numbered to make the alkene have the lowest possible number = -2-ene
- This means that the methyl groups are on carbons 2, 5 and 5 = 2,5,5-trimethyl
Answer 2:
- 4-Methyleneheptane
- The longest carbon chain is 7 carbons = hept
- The bonds within the longest chain are all single bonds = ane
- There is an alkene side chain on carbon 4 = 4-Methylene
- Note: There is an argument for this to be called 2-propylpent-1-ene as the alkene group typically is a high priority, however, this is not the correct systematic nomenclature
- The longest carbon chain is 7 carbons = hept
Answer 3:
- Propanal
- The longest carbon chain is 3 carbons = prop
- There is an aldehyde group = al
- By convention, the aldehyde group is attached to carbon-1
- The bonds within the main chain are all single bonds = an
Answer 4:
- 3-methylbutanal
- The longest carbon chain is 4 carbons = but
- There is an aldehyde group = al
- By convention, the aldehyde group is attached to carbon-1
- The bonds within the main chain are all single bonds = an
- There is a methyl side chain attached to carbon-3 = 3-methyl
Answer 5:
- Butanoic acid
- The longest carbon chain is 4 carbons = but
- There is a carboxylic acid group = -oic acid
- By convention, the carboxylic acid is attached to carbon-1
- The bonds within the main chain are all single bonds = an
Answer 6:
- 2-chlorobutane
- The longest carbon chain is 4 carbons = but
- The bonds within the main chain are all single bonds = an
- There is a chlorine atom attached to carbon-2 = 2-chloro
