Naming Hydrocarbons: Naming Alkynes
Contents
- Naming Hydrocarbons: Naming Alkynes
- Example:
- Question
- Identify the functional group
- Find the longest carbon chain containing the functional group
- Number the carbons in the longest chain
- Look for any branched groups, name them and assign the number of the carbon atom to which the group is attached
- Combine the elements of the name into a single word in the following order: branched groups; prefix; name ending according to the functional group and its position along the longest carbon chain
- Example:
- Question
- Identify the functional group
- Find the longest carbon chain containing the functional group
- Number the carbons in the longest chain
- Look for any branched groups
- Combine the elements of the name into a single word in the following order: branched groups; prefix; name ending according to the functional group and its position along the longest carbon chain
- Example:
The suffix for an alkyne is -yne.
Example:
Question
Give the IUPAC name for the following compound:
Identify the functional group
There is a triple bond between two of the carbon atoms, so this compound is an alkyne. The suffix will be -yne.
Find the longest carbon chain containing the functional group
The functional group is a triple bond, so the longest chain must contain the triple bond. There are six carbon atoms in the longest chain. The prefix of the compound’s name will be hex-.
Number the carbons in the longest chain
In this example, you will need to number the carbons from right to left so that the triple bond is between carbon atoms with the lowest numbers (the suffix for the compound will therefore be -2-yne).
Look for any branched groups, name them and assign the number of the carbon atom to which the group is attached
There is a methyl (\(\text{CH}_{3}\)) group attached to the fifth carbon (remember we have numbered the carbon atoms from right to left).
Combine the elements of the name into a single word in the following order: branched groups; prefix; name ending according to the functional group and its position along the longest carbon chain
If we follow this order, the name of the compound is 5-methylhex-2-yne.
Example:
Question
Give the IUPAC name for the following compound:
Identify the functional group
There are two triple bonds. The suffix will therefore be -diyne.
Find the longest carbon chain containing the functional group
The functional group is a triple bond, so the longest chain must contain all triple bonds. The longest carbon chain contains seven carbon atoms, therefore the prefix will be hept-.
Number the carbons in the longest chain
Numbering from left to right (shown in red) the first triple bond is on carbon 1 and the second is on carbon 5. The suffix will therefore be -1,5-diyne.
(Numbering from right to left (shown in blue) will give the suffix -2,6-diyne, and is incorrect).
Look for any branched groups
There are no branched groups for this molecule.
Combine the elements of the name into a single word in the following order: branched groups; prefix; name ending according to the functional group and its position along the longest carbon chain
The name of the compound is hept-1,5-diyne.
Example:
Question
Draw the structural and condensed structural formula for the organic compound
6-methylhept-3-yne
Identify the functional group
The suffix -3-yne means that this compound is an alkyne and there must be a triple bond located on carbon number 3.
Determine the number of carbon atoms in the longest chain containing the functional group
The prefix for the compound is hept- so there must be seven carbons in the longest chain.
Look for any branched groups
There is a methyl group located on carbon number 6.
Combine this information and add the hydrogen atoms
Condense the structural formula
First condense the main chain: \(\text{CH}_{3}\text{CH}_{2}\text{CCCH}_{2}\text{CHCH}_{3}\)
Then add the side chains (in brackets) on the relevant carbon atoms:
\(\text{CH}_{3}\text{CH}_{2}\text{CCCH}_{2}\text{CH}(\text{CH}_{3})\text{CH}_{3}\)