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Esters

01Esters

Structure and nomenclature

This section covers the ester functional group, ester structures and the rules used to name esters.

The ester group

Esters are carboxylic acid derivatives containing the ester group, −COO−\ce{-COO-}. An ester contains a carbonyl carbon joined to an oxygen atom that is bonded to another carbon group.

Methyl ethanoate

Condensed formula: CHX3COOCHX3\ce{CH3COOCH3}

Two parts of the name

The group joined to the single-bonded oxygen provides the alkyl name written first.

The part containing the carbonyl carbon is named from the parent carboxylic acid.

Naming esters

  1. Find the alkyl group attached to the single-bonded oxygen. This part originates from the alcohol.
  2. Find the carbon chain containing the C=O\ce{C=O} carbon. This part originates from the carboxylic acid.
  3. Change the acid ending -oic acid to -oate.
  4. Write the alcohol-derived alkyl name first, followed by the acid-derived alkanoate name.
Ester formula Alcohol-derived part Acid-derived part Name
CHX3COOCHX3\ce{CH3COOCH3} methyl ethanoate methyl ethanoate
CHX3COOCHX2CHX3\ce{CH3COOCH2CH3} ethyl ethanoate ethyl ethanoate
CHX3CHX2CHX2COOCHX2CHX3\ce{CH3CH2CH2COOCH2CH3} ethyl butanoate ethyl butanoate

Worked example: Name CHX3CHX2CHX2COOCHX2CHX3\ce{CH3CH2CH2COOCH2CH3}.

1. The group on the single-bonded oxygen is −CHX2CHX3\ce{-CH2CH3}, giving ethyl.

2. Counting the carbonyl carbon, the acid-derived chain contains four carbons, giving butanoate.

3. Put these parts together in the required order: ethyl butanoate.

Exam Tip: When drawing an ester, check the direction of the −COO−\ce{-COO-} linkage. The alkyl group named first must be joined to the single-bonded oxygen.

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