ORGANIC NOMENCLATURE GUIDELINES
number of C atoms 1C 2C 3C 4C 5C 6C
start of name meth eth prop but pent hex
functional group prefix suffix example name
H H H
alkane ane H C C C H propane
H H H
H H H H
alkene ene H C C C C H but-2-ene
C C
H H
H H H
F Br
fluoro / chloro
halogenoalkane H C C C H 2-bromopropane
Cl I / bromo / iodo
H Br H
H H H
alcohol O H hydroxy ol H C C C O H propan-1-ol
H H H
H H O
O
aldehyde * al H C C C H propanal
C H
H H
H H O H
O
ketone oxo one H C C C C H butanone
C
H H H
H O
O
carboxylic acid * oic acid H C C O H ethanoic acid
C O H
H
H H
nitrile * C N nitrile H C C C N propanenitrile
H H
H H H
H ethanamine
amine amino amine H C C N H
N H (ethylamine)
H H
H O
O
acyl chloride * oyl chloride H C C Cl ethanoyl chloride
C Cl
H
H O O H
O O
acid anhydride oic anhydride H C C O C C H ethanoic anhydride
C O C
H H
H H O H
O
ester oate H C C C O C H methyl propanoate
C O
H H H
H O H
O H
amide amide H C C N H ethanamide
C N H
H
* indicates this the C atom in this functional group is defined as carbon-1 in the chain
shading indicates that this prefix is only used if the suffix cannot be used
© www.CHEMSHEETS.co.uk 1 5-October-2023 Chemsheets AS 1223
,The naming of organic compounds is controlled by IUPAC (International Union of Pure and Applied Chemistry).
This gives a very systematic way of naming all organic molecules.
Some guidance on naming organic molecules
1 Longest C chain
• look at the molecule to find the longest C chain – if there is a functional group it must be the longest C
chain containing the functional group
• note that alkyl groups (e.g. methyl, ethyl, propyl) are not functional groups.
2 Number the C chain
• number the longest C chain (that contains the functional group) from the end that gives the functional
group(s) the lowest numbers
• note that some functional groups (labelled * in the chart, e.g. aldehyde group) are carbon-1 in the chain by
definition (and do not need a number themselves therefore), and define which end the numbers start for
other groups
• note that we should only include numbers in names when they are necessary – but we usually only omit
numbers in the simplest molecules where it is obvious that no number is needed
3 Putting the groups on the chain on the name
• groups that come off the C chain are given a number to show which C atom they are on (if necessary)
• when we write the name, these groups are listed in alphabetical order
• if there are several groups that are the same, then the prefix di (for two the same), tri (for three the same),
tetra (for four the same), etc are added first (note that the prefix di/tri/tetra/etc is ignored when we work out
alphabetical order)
Note
• numbers are separated by commas
• numbers and letters are separated by dashes
© www.CHEMSHEETS.co.uk 2 5-October-2023 Chemsheets AS 1223
, ALKANES
Structural formula Skeletal formula Name & comments
CH3 CH2 CH2 CH CH3 Longest C chain is 5C atoms – so it is a pentane
There is a methyl group coming off the chain. If the
CH3
chain is counted from the left end it is 4-methyl, but if
it is numbered from the right end if it 2-methyl which
Displayed formula
1 is a lower number.
H H H H H
2-methylpentane
H C C C C C H
H H H C H
H H
H
Structural formula Skeletal formula Name & comments
CH3 CH2 CH CH3 Longest C chain is 4C atoms – so it is a butane
There is a methyl group coming off the chain. If the
CH3 chain is counted from the left end it is 3-methyl, but if
it is numbered from the right end if it 2-methyl which
Displayed formula is a lower number.
2 However, the methyl group can only be on one of
H H H H the two central C atoms, and would be 2-methyl in
each case. It if was on one of the end C atoms, it
H C C C C H would be pentane and not methylbutane. As the
methyl group can only be on carbon-2, it does not
H H C H
need a number for its position.
H H
H
methylbutane
Structural formula Skeletal formula Name & comments
Longest C chain is 5C atoms – so it is a pentane
CH3 CH3
There are two methyl groups coming off the chain. If
CH3 CH CH CH2 CH3 the chain is counted from the left end they on
carbon-2 and carbon-3. If it is numbered from the
right end they on carbon-3 and carbon-4. Therefore
Displayed formula we number from the left end to get the lower
3 numbers.
H
H H
To show there are two methyl groups, we use di.
H C H H H
2,3-dimethylpentane
H C C C C C H
H H C H H
H H
H
Structural formula Skeletal formula Name & comments
CH3 Longest C chain is 5C atoms – so it is a pentane
There are two methyl groups coming off the chain. If
CH3 CH2 CH2 C CH3 the chain is counted from the left end they are both
on carbon-4. If it is numbered from the right end
CH3 they on are both on carbon-2. Therefore we number
from the right end to get the lower numbers.
Displayed formula
4 To show there are two methyl groups, we use di.
H
H H 2,2-dimethylpentane
H H H C H
H C C C C C H
H H H C H
H H
H
© www.CHEMSHEETS.co.uk 3 5-October-2023 Chemsheets AS 1223
number of C atoms 1C 2C 3C 4C 5C 6C
start of name meth eth prop but pent hex
functional group prefix suffix example name
H H H
alkane ane H C C C H propane
H H H
H H H H
alkene ene H C C C C H but-2-ene
C C
H H
H H H
F Br
fluoro / chloro
halogenoalkane H C C C H 2-bromopropane
Cl I / bromo / iodo
H Br H
H H H
alcohol O H hydroxy ol H C C C O H propan-1-ol
H H H
H H O
O
aldehyde * al H C C C H propanal
C H
H H
H H O H
O
ketone oxo one H C C C C H butanone
C
H H H
H O
O
carboxylic acid * oic acid H C C O H ethanoic acid
C O H
H
H H
nitrile * C N nitrile H C C C N propanenitrile
H H
H H H
H ethanamine
amine amino amine H C C N H
N H (ethylamine)
H H
H O
O
acyl chloride * oyl chloride H C C Cl ethanoyl chloride
C Cl
H
H O O H
O O
acid anhydride oic anhydride H C C O C C H ethanoic anhydride
C O C
H H
H H O H
O
ester oate H C C C O C H methyl propanoate
C O
H H H
H O H
O H
amide amide H C C N H ethanamide
C N H
H
* indicates this the C atom in this functional group is defined as carbon-1 in the chain
shading indicates that this prefix is only used if the suffix cannot be used
© www.CHEMSHEETS.co.uk 1 5-October-2023 Chemsheets AS 1223
,The naming of organic compounds is controlled by IUPAC (International Union of Pure and Applied Chemistry).
This gives a very systematic way of naming all organic molecules.
Some guidance on naming organic molecules
1 Longest C chain
• look at the molecule to find the longest C chain – if there is a functional group it must be the longest C
chain containing the functional group
• note that alkyl groups (e.g. methyl, ethyl, propyl) are not functional groups.
2 Number the C chain
• number the longest C chain (that contains the functional group) from the end that gives the functional
group(s) the lowest numbers
• note that some functional groups (labelled * in the chart, e.g. aldehyde group) are carbon-1 in the chain by
definition (and do not need a number themselves therefore), and define which end the numbers start for
other groups
• note that we should only include numbers in names when they are necessary – but we usually only omit
numbers in the simplest molecules where it is obvious that no number is needed
3 Putting the groups on the chain on the name
• groups that come off the C chain are given a number to show which C atom they are on (if necessary)
• when we write the name, these groups are listed in alphabetical order
• if there are several groups that are the same, then the prefix di (for two the same), tri (for three the same),
tetra (for four the same), etc are added first (note that the prefix di/tri/tetra/etc is ignored when we work out
alphabetical order)
Note
• numbers are separated by commas
• numbers and letters are separated by dashes
© www.CHEMSHEETS.co.uk 2 5-October-2023 Chemsheets AS 1223
, ALKANES
Structural formula Skeletal formula Name & comments
CH3 CH2 CH2 CH CH3 Longest C chain is 5C atoms – so it is a pentane
There is a methyl group coming off the chain. If the
CH3
chain is counted from the left end it is 4-methyl, but if
it is numbered from the right end if it 2-methyl which
Displayed formula
1 is a lower number.
H H H H H
2-methylpentane
H C C C C C H
H H H C H
H H
H
Structural formula Skeletal formula Name & comments
CH3 CH2 CH CH3 Longest C chain is 4C atoms – so it is a butane
There is a methyl group coming off the chain. If the
CH3 chain is counted from the left end it is 3-methyl, but if
it is numbered from the right end if it 2-methyl which
Displayed formula is a lower number.
2 However, the methyl group can only be on one of
H H H H the two central C atoms, and would be 2-methyl in
each case. It if was on one of the end C atoms, it
H C C C C H would be pentane and not methylbutane. As the
methyl group can only be on carbon-2, it does not
H H C H
need a number for its position.
H H
H
methylbutane
Structural formula Skeletal formula Name & comments
Longest C chain is 5C atoms – so it is a pentane
CH3 CH3
There are two methyl groups coming off the chain. If
CH3 CH CH CH2 CH3 the chain is counted from the left end they on
carbon-2 and carbon-3. If it is numbered from the
right end they on carbon-3 and carbon-4. Therefore
Displayed formula we number from the left end to get the lower
3 numbers.
H
H H
To show there are two methyl groups, we use di.
H C H H H
2,3-dimethylpentane
H C C C C C H
H H C H H
H H
H
Structural formula Skeletal formula Name & comments
CH3 Longest C chain is 5C atoms – so it is a pentane
There are two methyl groups coming off the chain. If
CH3 CH2 CH2 C CH3 the chain is counted from the left end they are both
on carbon-4. If it is numbered from the right end
CH3 they on are both on carbon-2. Therefore we number
from the right end to get the lower numbers.
Displayed formula
4 To show there are two methyl groups, we use di.
H
H H 2,2-dimethylpentane
H H H C H
H C C C C C H
H H H C H
H H
H
© www.CHEMSHEETS.co.uk 3 5-October-2023 Chemsheets AS 1223
