AQA · A-Level · Chemistry
Course version: 7405 · Version from Sept 2016
The structures of: acid anhydrides acyl chlorides amides.
Full specification wording
Acylation (A-level only): The structures of: acid anhydrides acyl chlorides amides.
All three are relatives of the carboxylic acid with the -OH replaced.
Checked against the AQA 7405 specification (opens in a new tab) on .
- Point 1 of 5
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
All three are relatives of the carboxylic acid with the -OH replaced. An acyl chloride is RCOCl, the chlorine bonded to the carbonyl carbon, named -oyl chloride, as in ethanoyl chloride. An acid anhydride is two acyl groups sharing a single oxygen, (RCO)₂O, and is what is left when two acid molecules lose one molecule of water between them, hence ethanoic anhydride. An amide has nitrogen on the carbonyl carbon, RCONH₂, named -amide; if an alkyl group replaces one of the hydrogens on the nitrogen the name gains an N- prefix, as in N-methylethanamide. Reactivity falls along the series acyl chloride, anhydride, ester, amide, because the group leaving the carbonyl carbon becomes harder to displace.
What earns the marks
- The acyl chloride drawn with chlorine bonded to the carbonyl carbon.
- The anhydride drawn as two C=O groups joined through a single oxygen atom.
- The amide drawn with nitrogen bonded to the carbonyl carbon.
- The correct IUPAC name, ending -oyl chloride, anhydride or -amide as appropriate.
Common mistakes and how to put them right
Bonding the chlorine to the carbonyl oxygen instead of the carbon.
Drawing an anhydride with an O-O link, which is a peroxide.
Naming CH₃COCl as ethanol chloride or as ethyl chloride.
Drawing the bond from the carbon chain to the O of -COCl, which AQA marks as an ambiguous structure.
Exam tips
- Always draw the bond to the carbon of a carbon-containing functional group; the bond to an oxygen there is penalised even when the rest is right.
- An N- prefix in an amide name tells you the group is on the nitrogen, not on the carbon chain.
Try the lesson
The start of the Acylation (A-level only): The structures of: acid anhydrides acyl chlorides amides. lesson, made from checked teaching notes for this specification point.
Have a go first
Which functional group is present in an acyl chloride such as ethanoyl chloride?
Listen
All three are relatives of the carboxylic acid with the -OH replaced. An acyl chloride is RCOCl, the chlorine bonded to the carbonyl carbon, named -oyl chloride, as in ethanoyl chloride. An acid anhydride is two acyl groups sharing a single oxygen, (RCO)₂O, and is what is left when two acid molecules lose one molecule of water between them, hence ethanoic anhydride. An amide has nitrogen on the carbonyl carbon, RCONH₂, named -amide; if an alkyl group replaces one of the hydrogens on the nitrogen the name gains an N- prefix, as in N-methylethanamide. Reactivity falls along the series acyl chloride, anhydride, ester, amide, because the group leaving the carbonyl carbon becomes harder to displace. A strong answer earns marks for these points. the acyl chloride drawn with chlorine bonded to the carbonyl carbon. the anhydride drawn as two C=O groups joined through a single oxygen atom. the amide drawn with nitrogen bonded to the carbonyl carbon. the correct IUPAC name, ending -oyl chloride, anhydride or -amide as appropriate. Exam tip: Always draw the bond to the carbon of a carbon-containing functional group; the bond to an oxygen there is penalised even when the rest is right.
See it
Key words
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acyl chloride
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acid anhydride
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amide
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order of reactivity
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See every definition
- acyl chloride
- A compound RCOCl in which the chlorine is bonded to the carbonyl carbon, named -oyl chloride, as in ethanoyl chloride.
- acid anhydride
- Two acyl groups sharing a single oxygen, (RCO)₂O, left when two acid molecules lose one molecule of water between them, hence ethanoic anhydride.
- amide
- A compound with nitrogen on the carbonyl carbon, RCONH₂, named -amide, gaining an N- prefix if an alkyl group replaces one of the hydrogens on the nitrogen.
- order of reactivity
- Reactivity falls along the series acyl chloride, anhydride, ester, amide, because the group leaving the carbonyl carbon becomes harder to displace.
Label the diagram
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1Box 1
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3Box 3
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