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CHEM 131
How to name organic hydrocarbons – A quick tutorial
Prefix
Root
The position & type
of functional groups
The longest chain
Ending
Class of compound
Always be systematic and do all the steps in order until you are comfortable with naming
compounds. Skipping steps while you are learning how to name molecules can make it more
confusing than it needs to be.
# of C’s
1
2
3
4
5
6
7
8
9
10
As “Longest Chain”
Condensed Formula
Alkane Root
Name
CH4
methane
CH3-CH3
ethane
CH3-CH2-CH3
propane
CH3-CH2-CH2-CH3
butane
CH3-CH2-CH2-CH2-CH3
pentane
CH3-(CH2)4-CH3
hexane
CH3-(CH2)5-CH3
heptane
CH3-(CH2)6-CH3
octane
CH3-(CH2)7-CH3
novane
CH3-(CH2)8-CH3
decane
As “Functional Group”
Condensed Formula
Alkyl Name
-CH4
-CH2-CH3
-CH2-CH2-CH3
-CH2-CH2-CH2-CH3
-CH2-CH2-CH2-CH2-CH3
-(CH2)5-CH3
-(CH2)6-CH3
-(CH2)7-CH3
-(CH2)8-CH3
-(CH2)9-CH3
methyl
ethyl
propyl
butyl
pentyl
hexyl
heptyl
octyl
novyl
decyl
Step 1: Identify the longest chain (root name)

Remember the longest chain is not necessarily straight across (it can be drawn with a few
bends in the chain)
Cyclopentane

For cycloalkanes, the longest chain is the ring


For alkenes or alkynes, the double or triple bond has to be part of the chain
Write down the base name. For example: nonane
Step 2: Number the longest chain
 Find the combination that will give the lowest set of numbers for all branches or functional
groups.
 For alkanes you are looking for the overall lowest set of numbers. For all other functional
groups you want the lowest number possible for the functional group, ie the alkene and the
alkyne number should be as low as possible.
Maxi Boeckl 4/20/10
CHEM 131
nonane
1
5
5
6
7
8
9
4
1
2
1
2
3
3
2
Cyclopentane
6
4
5
3
4
1-hexene
Step 3: Identify the location of the functional groups and identify them
 When naming the functional group, do not count any of the carbons that were already
included in the longest chain.
 Write down the # (location) – with the functional group next to it.
 Looking at example 1:
nonane
o 2-methyl
7
9
8
6
5
o 4-butyl
o 6-methyl
1



2
3
4
Example 2:
o 1-butyl (do not count the C that is part of the ring –
you already accounted for that one by including that
in cyclopentane)
o 2-methyl
Example 3:
o 1 ene (double and triple bonds are considered
functional groups)
o 2-methyl
o 3-ethyl
o Two 4-methyl groups
1'
C
2'
4'
3'
Cyclopentane
1
2
3
6
4
5
1-hexene
At this point if you have more than one of the same groups, start grouping them together.
Remember to use the prefixes di-, tri-, tetra- etc. Remember that alkenes are also functional
groups and you would name multiple double bonds -diene and -triene, etc.
o For example 1, this would give : 2,6-dimethyl
o For example 2, this would give: 2,4,4-trimethyl
Step 4: Put all the different part together
 Before putting the functional groups in front of the root name, alphabetize the functional
groups. Remember to ignore the prefix di-, tri-, tetra- etc.
 The three examples are:
o 4-butyl-2,6-dimethylnonane
o 1-butyl-2-methylcyclopentane
o 3-ethyl-2,4,4-trimethyl-1-hexene
Some more examples:
You will start numbering from the left (end closest to triple bond). As with
alkenes, the C-C triple bond has to be part of the longest chain. There are
6 carbons with the triple bond at position 2 and a methyl at position 4.
Name: 4-methyl-2-hexyne
C
C
In this example you have a benzene ring with two branches, 2 ethyl groups at
positions 1 and 3. Since this benzene ring is not one of the common base
groups used with benzene rings, the name would be 1,3-diethylbenzene.
Maxi Boeckl 4/20/10
CHEM 131
OH
Compare this to the following, where we have phenol (shown in red) as
the base name with an additional ethyl group. Thus 3-ethylphenol.
Review your aromatic base names!
Finally, last example:
Again we have 5 carbons in the longest chain, with the double bond
being at position 2. Remember, you number so that the double bond has
the lowest number. This would put the methyl in position 4. The double
bond is trans, so we need to include that in the name.
Name: 4-methyl-trans-2-pentene
Maxi Boeckl 4/20/10