Isomers of alkanols are classified depending on the location of the -OH functional group
Classification
(o)
General Formula
Location of -OH group
Primary
1o
R-OH
terminal carbon atom
Secondary
2o
R2-CHOH
carbon atom is bonded to 2 other carbon atoms
Tertiary
3o
R3-C-OH
carbon atom is bonded to 3 other carbon atoms
Animated Tutorial
Examples
Primary Alkanols
Name the alkanol shown below:
H |
H |
H |
H |
H-
C
-
C
-
C
-
C
-OH
| H
| H
| H
| H
Number the longest carbon chain that includes the -OH functional group:
H |
H |
H |
H |
H-
(4)C(1)
-
(3)C(2)
-
(2)C(3)
-
(1)C(4)
-OH
| H
| H
| H
| H
Numbering from left to right (red numbers) : -OH group attached to carbon 4.
Numbering from right to left (blue numbers): -OH group attached to carbon 1.
The longest carbon chain is numbered so that the -OH group is attached to the carbon with the lowest number, ie 1-.
There are 4 carbon atoms in the longest chain, so the prefix is but-
There are only single bonds between the carbon atoms in the chain so the middle of the name is -an-
The suffix is -ol
The name of the molecule is 1-butanol
Secondary Alkanols
Name the molecule shown below:
H |
H |
H |
H |
H-
C
-
C
-
C
-
C
-H
| H
| OH
| H
| H
Number the longest carbon chain that includes the -OH functional group:
H |
H |
H |
H |
H-
(4)C(1)
-
(3)C(2)
-
(2)C(3)
-
(1)C(4)
-H
| H
| OH
| H
| H
Numbering from left to right (red numbers) : -OH group attached to carbon 2.
Numbering from right to left (blue numbers): -OH group attached to carbon 3.
The longest carbon chain is numbered so that the -OH group is attached to the carbon with the lowest number, ie 2-.
There are 4 carbon atoms in the longest chain, so the prefix is but-
There are only single bonds between the carbon atoms in the chain so the middle of the name is -an-
The suffix is -ol
The name of the molecule is 2-butanol
Tertiary Alkanols
Name the compound shown below:
H |
H |
H-C-H |
H |
H-
C
-
C
-
C
-H
| H
| OH
| H
Number the longest carbon chain that includes both the side-chain (branch) and the -OH functional group:
H |
H |
H-C-H |
H |
H-
(3)C(1)
-
(2)C(1)
-
(1)C(1)
-H
| H
| OH
| H
Numbering from left to right or from right to left result in the same numbers in this example, the -OH group and the side-chain are both attached to carbon 2.
Name and number the side chain as for branched chain alkanes: CH3 is a methyl group attached to carbon 2 so we have 2-methyl
Name the longest carbon chain: 3 carbon atoms = prop-
Only single bonds between carbon atoms in the chain so the middle of the name is -an-
The -OH functional group means the suffix of the name is ol and it is attached to carbon 2
The molecule's name is 2-methyl-2-propanol
Diols
Name the molecule shown below:
H |
H |
H |
H |
H-
C
-
C
-
C
-
C
-OH
| H
| OH
| H
| H
Number the longest carbon chain to include both -OH functional groups:
H |
H |
H |
H |
H-
(4)C(1)
-
(3)C(2)
-
(2)C(3)
-
(1)C(4)
-OH
| H
| OH
| H
| H
Numbering from left to right (red numbers) : -OH groups attached to carbons 2 and 4.
Numbering from right to left (blue numbers): -OH groups attached to carbons 1 and 3.
The longest carbon chain is numbered so that the -OH groups are attached to the carbon atoms with the lowest number combination, ie 1,3-.
There are 4 carbon atoms in the longest chain, so the prefix is but-
There are only single bonds between the carbon atoms in the chain so the middle of the name is -ane-
There are 2 -OH groups so the suffix is -diol
The name of the molecule is 1,3-butanediol
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