Esters: alkyl alkanoate
An ester is made from an alcohol and a carboxylic acid. Its name has two words: the alkyl group from the alcohol first, then the acid part with -oic acid changed to -oate.
- Find the C=O. The chain that includes the C=O carbon is the acid part.
- The group on the other side of the single-bonded O is the alcohol part. Name it as an alkyl group.
- Write: alkyl + space + acid name ending in -oate.
Reading the name back: in propyl ethanoate, the propyl is on the O and the ethanoate (two carbons, including C=O) is the acid part. Its isomer ethyl propanoate is a different compound.
Amides: -amide
Replace -oic acid with -amide. Groups on the nitrogen get N- as their locant.
Acyl chlorides: -oyl chloride
Replace -oic acid with -oyl chloride: ethanoyl chloride, propanoyl chloride, benzoyl chloride.
Acid anhydrides: -oic anhydride
Two acid units joined through an O. If both halves are the same, replace "acid" with anhydride: ethanoic anhydride.
Nitriles: -nitrile
Count the carbon of the C≡N as part of the chain, and add -nitrile to the alkane name: CH₃CN is ethanenitrile, CH₃CH₂CN is propanenitrile.
Common mistakes
- Swapping the two halves of an ester name. The alkyl group on the O always comes first.
- Not counting the C=O carbon (or the C≡N carbon) as part of the chain.
- Writing "methylethanamide" when the methyl is on N. It's N-methylethanamide.
Quick answers
How do you name an ester?
Name the alkyl group from the alcohol first, then the acid part with -oic acid changed to -oate. CH₃COOCH₂CH₃ is ethyl ethanoate.
What is the difference between ethyl propanoate and propyl ethanoate?
They are isomers. Ethyl propanoate is CH₃CH₂COOCH₂CH₃ (propanoic acid with an ethyl group on O). Propyl ethanoate is CH₃COOCH₂CH₂CH₃ (ethanoic acid with a propyl group on O).
What does N- mean in an amide name?
N- shows that a group is attached to the nitrogen, not to a carbon. N-methylethanamide has a methyl group on the nitrogen of ethanamide.
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