Naming and drawing carboxylic acids, esters, amides and acyl chlorides
-oic acid, -oate, -amide and -oyl chloride names: where C1 is, how ester names split into two words, and how N-substituents are shown.
Carboxylic acids and their derivatives all contain a carbonyl carbon bonded to a heteroatom: –COOH in acids, –COOR in esters, –CONR2 in amides and –COCl in acyl chlorides. In every case the carbonyl carbon is C1 of the parent chain, so these suffixes never need a locant on a chain.
Carboxylic acids: -oic acid
Replace the final -e of the alkane with -oic acid. The carboxyl carbon is counted in the chain: ethanoic acid (acetic acid) has two carbons, propanoic acid three.
Two COOH groups give a -dioic acid: butanedioic acid has a COOH at each end of a four-carbon chain. For rings, the COOH carbon is outside the ring and the suffix is -carboxylic acid; the benzene compound is benzoic acid.
Esters: two words, read backwards
An ester is made from an acid and an alcohol, and its name reflects that. The first word is the alkyl group on the single-bonded oxygen (from the alcohol). The second word is the acid part, with -oic acid changed to -oate.
Worked example: ethyl propanoate
"Propanoate" is a three-carbon acid part: CH3CH2–C(=O)–O–. "Ethyl" is attached to that oxygen. The carbonyl carbon belongs to the propanoate, not to the ethyl group.
Reversing the two parts gives a different compound with the same formula. Propyl ethanoate, CH3C(=O)OCH2CH2CH3, is an isomer of ethyl propanoate:
Amides: -amide
Replace -e with -amide: ethanamide is CH3CONH2. Groups attached to the nitrogen are given the locantN instead of a number: N-methylethanamide has one methyl on nitrogen, and N,N-dimethylethanamide has two.
Acyl chlorides: -oyl chloride
Replace -oic acid with -oyl chloride: ethanoyl chloride (acetyl chloride) is CH3COCl, with Cl on the carbonyl carbon.
Which group gets the suffix?
When several groups are present, the one with the highest seniority becomes the suffix and the others are prefixes. For the groups on this site the order is: carboxylic acid > ester > acyl halide > amide > nitrile > aldehyde > ketone > alcohol > amine. Halogens and alkyl groups are always prefixes.
Common mistakes
- Leaving the carboxyl carbon out of the count. Propanoic acid has three carbons in total, including the COOH carbon.
- Swapping the parts of an ester name. In methyl ethanoate the methyl is on oxygen and the ethanoate carries the C=O.
- Putting N-substituents on carbon. In N-methylethanamide the methyl is on nitrogen; with that methyl on carbon instead you would have propanamide, a different compound.
- Drawing the carboxylate ion. "Acid" means the neutral –COOH. –COO− is a different species, and the checker treats it as one.