Chemistry » Organic Molecules » IUPAC Naming And Formulae

# Naming Alkynes

## Naming Hydrocarbons: Naming Alkynes

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.

### 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:

$$\text{CH}_{3}\text{CH}_{2}\text{CCCH}_{2}\text{CH}(\text{CH}_{3})\text{CH}_{3}$$