Organic Chemistry · Carboxylic Acid Derivatives: Nucleophilic Acyl Substitution Reactions
Naming Carboxylic Acid Derivatives
On this page 9 sections
In 30 seconds
Carboxylic acid derivatives share the Acyl group R–CO–: carbonyl carbon bonded to a carbon chain Full entry → R–CO– (a carbonyl carbon bonded to a carbon chain) attached to a leaving group Z:
- Acid halides: R–CO–X (X = Cl, Br)
- Acid anhydrides: R–CO–O–CO–R′
- Esters: R–CO–O–R′
- Amides: R–CO–NH₂, R–CO–NHR′, R–CO–NR′₂
- Nitriles: R–C≡N (formally a derivative because it hydrolyzes to the acid)
Naming each family follows one rule: start from the parent carboxylic acid name and change the ending (or add the alkyl name for esters). This topic gives the systematic (IUPAC) names, the common names you will still see (acetic acid, acetyl chloride), and the priority rules that decide which group gets the suffix when several are present.
Why this matters
- Names are the map. Every reaction in this chapter is described as "acid chloride to Ester R–CO–O–R′: acyl group + alkoxy group Full entry →," "Amide R–CO–NR′₂: acyl group + nitrogen Full entry → to nitrile," and so on; misreading a name means misreading the reactivity.
- Pharma and biology vocabulary: Aspirin is an ester (acetylsalicylic acid); paracetamol is an amide; penicillin contains an amide (β-lactam); fats are esters of glycerol. Recognizing the functional class from the name predicts its chemistry.
- IUPAC vs. common names: Textbooks, patents, and drug labels mix both systems; you must be fluent in both.
- Nomenclature is a scored skill: "Name the compound" and "draw the structure from the name" questions are guaranteed exam items in every organic course.
- No special safety issues beyond standard lab practice — this topic is language, not reagents.
The college version
Core Concepts
Acid halides: –oyl halides
Replace the "-oic acid" ending with "-oyl halide," and name the halogen as a separate word:
| Parent acid | Acid halide |
|---|---|
| Ethanoic acid (acetic) | Ethanoyl chloride (acetyl chloride), CH₃COCl |
| Benzoic acid | Benzoyl chloride, C₆H₅COCl |
| Propanedioic acid | Propanedioyl dichloride (from dicarboxylic acids) |
The carbonyl carbon is always carbon 1; the halide is not a substituent — it is part of the parent name.
Acid anhydrides: name both acids
An Anhydride R–CO–O–CO–R′: two acyl groups on one oxygen Full entry → is two acyl groups joined by an oxygen. Symmetric anhydrides are named from the parent acid by replacing "acid" with "anhydride":
- Ethanoic acid → ethanoic anhydride (acetic anhydride), (CH₃CO)₂O
- Benzoic acid → benzoic anhydride, (C₆H₅CO)₂O
Unsymmetrical anhydrides name both acids in alphabetical order: ethanoic propanoic anhydride, CH₃CO–O–COCH₂CH₃. Cyclic anhydrides (from dicarboxylic acids) use the acid name too: succinic acid → succinic anhydride.
Esters: alkyl alkanoate
Esters get a two-word name: first the alkyl group from the alcohol part (R′–), then the acid name with "-oic acid" changed to "-oate":
- Ethanol + ethanoic acid → ethyl ethanoate (ethyl acetate), CH₃COOCH₂CH₃
- Methanol + benzoic acid → methyl benzoate, C₆H₅COOCH₃
- Butan-1-ol + propanoic acid → butyl propanoate, CH₃CH₂COOCH₂CH₂CH₂CH₃
The alcohol-derived group comes first (as a substituent on the oxygen), and the carbonyl carbon is carbon 1 of the acid part. Common names keep the common acid name: acetic acid → acetate, formic acid → formate.
Amides: –amide
Replace "-oic acid" with "-amide" and name substituents on nitrogen with N- prefixes:
- Ethanoic acid → ethanamide (acetamide), CH₃CONH₂
- N-methyl substitution: N-methylethanamide, CH₃CONHCH₃
- N,N-dimethyl: N,N-dimethylethanamide, CH₃CON(CH₃)₂
Primary amides end in –amide (NH₂); secondary and tertiary amides carry N-alkyl groups. Cyclic amides are lactams (e.g., the β-lactam ring of penicillins).
Nitriles: –nitrile or cyano-
As the parent, add "-nitrile" to the alkane name of the same carbon count: butanenitrile, CH₃CH₂CH₂CN; benzonitrile, C₆H₅CN. As a substituent on a chain with a higher-priority group, use cyano-: 3-cyanopropanoic acid, NC–CH₂CH₂–COOH.
Priority order: which group gets the suffix
When a molecule contains several functional groups, the highest-priority group becomes the suffix and all others become prefixes:
Carboxylic acid > anhydride > ester > Acid halide R–CO–X: acyl group + halogen Full entry → > amide > nitrile > aldehyde > ketone > alcohol > amine
Example: a molecule with both an ester and a nitrile is named as the ester (higher priority), with the nitrile as a cyano substituent: methyl 3-cyanopropanoate. This priority list is the tie-breaker in nearly every naming problem.
Common Confusions
| Do Not Confuse | With | Difference |
|---|---|---|
| Ethyl ethanoate (ester) | Ethanoyl chloride (acid halide) | –oate ending = ester (alkoxy group); –oyl chloride = acid halide (halogen) |
| Acid anhydride | Ester | Anhydride is two acyl groups on one oxygen; ester is one acyl group on an alkoxy group |
| N-methylpropanamide | 2-methylpropanamide | N- means on nitrogen; a number means on the carbon chain |
| Butanenitrile (parent) | Cyano substituent | –nitrile as parent when it is the highest-priority group; cyano- as prefix when a higher group exists |
| Common vs. IUPAC names | — | Acetic acid = ethanoic acid; acetyl chloride = ethanoyl chloride; both systems are used in the wild |
| Ester priority vs. amide priority | Guessing the order | The standard seniority list is acid > anhydride > ester > acid halide > amide > nitrile — ester outranks amide; memorize the order, don't guess |
Eli explains
The same idea, in plain words
Explain it like I’m 10
Naming acid derivatives is like naming a family: everyone shares the same last name (the parent acid), and the first name tells you which "child" it is — chloride, anhydride, ester, amide, or nitrile. For esters, you add where the alcohol "lives" first (like a first name), then the acid family name. Once you know the family, you know the personality: acid halides are the most reactive, amides the calmest.
Worked example
Example 1: Naming from structure
Name each compound systematically: (a) CH₃CH₂COCl; (b) (CH₃CH₂CO)₂O; (c) CH₃CH₂COOCH₃; (d) CH₃CH₂CONH₂; (e) CH₃CH₂CH₂CN.
(a) The parent acid is propanoic acid; replacing –oic acid with –oyl chloride gives propanoyl chloride. (b) Two propanoyl groups on one oxygen: propanoic anhydride. (c) Two parts: methyl (from the alcohol) + propanoate (from propanoic acid): methyl propanoate. (d) Propanoic acid → propanamide. (e) Four carbons in the chain ending in –nitrile: butanenitrile.
Example 2: Drawing structures from names
Draw the structure of (a) N,N-dimethylbenzamide; (b) ethyl butanoate; (c) benzoyl chloride.
(a) Benzoic acid's acyl group (C₆H₅CO–) on a nitrogen bearing two methyl groups: C₆H₅–CO–N(CH₃)₂. The N,N- tells you both methyls sit on nitrogen, not on the ring. (b) Ethyl group (CH₃CH₂–) on the oxygen of butanoate: CH₃CH₂CH₂–CO–O–CH₂CH₃. (c) C₆H₅–CO–Cl: benzene ring, carbonyl carbon, chlorine — benzoyl chloride.
Example 3: Applying the priority order
Name the compound NC–CH₂CH₂–COOCH₃.
Step 1 — Find the highest-priority group. The molecule has an ester (methyl ester) and a nitrile. In the priority list, ester ranks above nitrile, so the parent is the ester.
Step 2 — Number the chain. The carbonyl carbon of the ester is C1; the nitrile carbon is C3 (NC–CH₂–CH₂–COOCH₃ → C3 is the –CH₂ bearing the –CN; the nitrile carbon itself is not part of the parent chain).
Step 3 — Name it. Parent: methyl propanoate (three-carbon chain from C1); substituent at C3: cyano. Full name: methyl 3-cyanopropanoate.
Key takeaways
- Acid halide: –oyl halide (ethanoyl chloride); carbonyl carbon is C1.
- Anhydride: name from the acid(s): ethanoic anhydride; unsymmetrical ones list both acids alphabetically.
- Ester: alkyl (alcohol part) + alkanoate (acid part): ethyl ethanoate.
- Amide: –amide; N-substituents get N- prefixes: N-methylpropanamide.
- Nitrile: –nitrile as parent (butanenitrile); cyano- as substituent (3-cyanopropanoic acid).
- Priority order: acid > anhydride > ester > acid halide > amide > nitrile > aldehyde > ketone > alcohol > amine — the highest group is the suffix.
- Common names persist: acetic/acetate, formic/formate, benzoic/benzoate, acetyl chloride.
Check yourself
6 review questions from the chapter. Try each one, then open the answer.
Name CH₃COCl, (CH₃CO)₂O, CH₃COOCH₂CH₃, and CH₃CONH₂ systematically.
Show answer
Ethanoyl chloride; ethanoic anhydride; ethyl ethanoate; ethanamide.
What is the difference between N-methylpropanamide and 2-methylpropanamide?
Show answer
N-methylpropanamide has a methyl group on nitrogen; 2-methylpropanamide has one on carbon 2 of the chain.
Name the ester made from methanol and butanoic acid; from ethanol and benzoic acid.
Show answer
Methyl butanoate; ethyl benzoate.
In NC–CH₂CH₂–COOH, which group is the suffix and which the prefix? Name the compound.
Show answer
The carboxylic acid is the suffix (highest priority); the nitrile is the cyano prefix. Name: 3-cyanopropanoic acid.
Give the common name for ethanoyl chloride and for ethanoic anhydride.
Show answer
Acetyl chloride; acetic anhydride.
Why is the carbonyl carbon numbered C1 in acid derivatives?
Show answer
The carbonyl carbon defines the functional group and gets the lowest possible number (1), matching how the acid is numbered.
Study tools & related lessonsKey vocabulary · Related
Key vocabulary
- Acyl group
- R–CO–: carbonyl carbon bonded to a carbon chain
- Acid halide
- R–CO–X: acyl group + halogen
- Anhydride
- R–CO–O–CO–R′: two acyl groups on one oxygen
- Ester
- R–CO–O–R′: acyl group + alkoxy group
- Amide
- R–CO–NR′₂: acyl group + nitrogen
- Lactam
- Cyclic amide
- Suffix vs. prefix
- Ending name vs. substituent name
- N- prefix
- Marks alkyl groups on the amide nitrogen
Sources & references
This lesson was adapted from the open educational references above; their licenses and attributions are preserved. See Copyright & Licensing.
Educational content only. It is not medical, legal or professional advice. Found an error? Tell us.