Carboxylic Acid Derivatives

Organic Chemistry

Nomenclature
Isomers
Bonding
Analyzing Organic Reactions
Alcohols
Aldehydes and Ketones I
Aldehydes and Ketones II - Enolate Chemistry
Carboxylic Acids
Carboxylic Acid Derivatives
Nitrogen- and Phosphorus-Containing Compounds
Spectroscopy
Separations and Purifications
High-Yield Cheat Sheet

Progress

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Chapter 9: Carboxylic Acid Derivatives

Updated Apr 17, 2026

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🎯 Diagnostic: Test Your Starting Level 24 questions (2 per section). No prior reading required, see what you already know.

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1. (9.1) Carboxylic acid derivatives share the R-C(=O)-X structure, where X is:

A) A heteroatom such as Cl, OR', OCOR', or NR'₂ that can leave
B) Always hydrogen
C) Only oxygen
D) Always carbon

A. Different X groups give acyl halides, anhydrides, esters, and amides.

2. (9.1) Interconversion between derivatives runs naturally:

A) Never
B) From more reactive to less reactive (acid chloride → anhydride → ester → amide); the reverse direction requires activation
C) Randomly
D) Only among esters

B. Thermodynamics drives "downhill" conversions. To go uphill, we activate the acid (e.g., SOCl₂) first.

3. (9.2) Acyl halides (R-COCl):

A) Are the least reactive derivatives
B) Contain nitrogen
C) Are the most reactive derivatives; readily converted to other derivatives
D) Cannot be made from acids

C. Because of their reactivity, acyl chlorides are often made in situ and used immediately.

4. (9.2) Acyl chlorides are typically made from carboxylic acids using:

A) Water
B) NaOH
C) A strong base
D) SOCl₂ or PCl₅ (or oxalyl chloride)

D. SOCl₂ is clean because the byproducts (SO₂ and HCl gas) bubble away.

5. (9.3) An anhydride has the structure:

A) R-CO-O-CO-R', two acyl groups joined by an oxygen
B) R-O-R' (ether)
C) R-CO-NH₂
D) R-COCl

A. Acetic anhydride is widely used in synthesis (e.g., acetylation of salicylic acid to aspirin).

6. (9.3) Anhydrides are conveniently made by:

A) Hydrolysis
B) Dehydration of two carboxylic acids or, better, acid chloride + carboxylate
C) Oxidation
D) Grignard reaction

B. Direct dehydration of two acids requires harsh conditions; acid chloride + carboxylate is cleaner.

7. (9.4) Esters (R-COOR') are typically made by:

A) Amine addition to a carbonyl
B) Base hydrolysis
C) Fischer esterification (acid + alcohol, acid-catalyzed) or acyl chloride + alcohol
D) Reduction of a carbonyl

C. Acid chlorides are preferred when the carboxylic acid is sensitive to acid-catalyzed conditions.

8. (9.4) Saponification refers to:

A) Acid-catalyzed hydrolysis
B) Ester reduction
C) Ester oxidation
D) Base-catalyzed (irreversible) hydrolysis of an ester, producing carboxylate and alcohol

D. This is how soaps are made: NaOH hydrolyzes triglycerides to glycerol plus fatty-acid sodium salts.

9. (9.5) Amides (R-CO-NR'₂):

A) Are the least reactive of the standard derivatives; N lone pair donates strongly into the carbonyl, deactivating it
B) Are more reactive than acyl chlorides
C) Are ionic
D) Are radicals

A. This lack of reactivity is essential for peptide bond stability in proteins.

10. (9.5) Amides have restricted rotation about the C-N bond because:

A) There is no resonance
B) The N lone pair donates into C=O, giving the C-N partial double-bond character
C) Amides are ionic
D) N is sp³

B. Peptide bonds in proteins are planar because of this partial double-bond character (Ramachandran space).

11. (9.6) The reactivity ladder (most → least reactive) is:

A) Amides > esters > anhydrides > acid chlorides
B) Esters > amides > acid chlorides
C) Acid chlorides > anhydrides > esters > amides (tracks leaving-group stability and X electron donation)
D) Acids > anhydrides > esters

C. Better LG + weaker π donation = more reactive carbonyl.

12. (9.6) Moving "up" the reactivity ladder (e.g., ester → anhydride) requires:

A) No change
B) Passive hydrolysis
C) Just water
D) Activation (e.g., convert to acid chloride first), because the step is thermodynamically uphill

D. Uphill conversions need a high-energy intermediate or coupling reagent.

13. (9.7) Nucleophilic acyl substitution (NAS) proceeds by:

A) Nucleophile attack on the carbonyl carbon to form a tetrahedral intermediate, then loss of the leaving group
B) Radical chain
C) Concerted SN2
D) Pericyclic rearrangement

A. Addition-elimination at an sp² center. Rate depends on both nucleophile strength and leaving-group ability.

14. (9.7) The rate of NAS depends on:

A) Heat only
B) Both the electrophilicity of the carbonyl and the leaving-group ability of X
C) Solvent polarity only
D) Temperature only

B. Two rates are actually in play: addition of nucleophile and elimination of leaving group.

15. (9.8) Because amides are less reactive than esters:

A) The conversion ester → amide is impossible
B) A strong base is always required
C) An ester + amine can form the amide (often with heat); the reverse (amide → ester) requires activation
D) LiAlH₄ is needed

C. Aminolysis of an ester goes downhill on the reactivity ladder.

16. (9.8) Acid chloride + carboxylate salt gives:

A) No product
B) An aldehyde
C) An alcohol
D) An anhydride (R-CO-O-CO-R'), a classic route to mixed anhydrides

D. Carboxylate attacks the acyl chloride, displacing Cl⁻.

17. (9.9) Hydrolysis of a carboxylic acid derivative produces:

A) The parent carboxylic acid plus the leaving group (X-H)
B) An alcohol
C) A free radical
D) An ester

A. Water is the nucleophile; the acid is regenerated along with Cl⁻, amine, or alcohol depending on the derivative.

18. (9.9) Acidic hydrolysis of an amide:

A) Is very fast at room temperature
B) Needs harsh conditions: strong aqueous acid (or base) and heat, because amides are the least reactive derivative
C) Requires nothing
D) Produces only gas

B. Amide stability is why proteases use elaborate active-site chemistry to cleave peptide bonds quickly under mild conditions.

19. (9.10) Acyl chloride + amine:

A) Does not react
B) Reaches equilibrium
C) Rapidly forms an amide; a base (e.g., pyridine, Et₃N) is often added to absorb the HCl produced
D) Gives an ether

C. Fast, high-yield acylation. Without added base, excess amine must act as the HCl scavenger.

20. (9.10) Esters + amines (without a catalyst):

A) React instantly
B) Form anhydrides
C) Yield amines back
D) React slowly; usually heated to deliver the amide + alcohol

D. Kinetics are slow without activation. DMAP and other catalysts accelerate the reaction.

21. (9.11) Acyl chloride + alcohol rapidly gives:

A) An ester (fast acylation; pyridine or Et₃N is often added to soak up HCl)
B) An amide
C) An aldehyde
D) No reaction

A. Vs. Fischer esterification, this route is fast and irreversible.

22. (9.11) Transesterification involves:

A) Acid chloride swap
B) Replacing one ester's -OR with a different -OR' using an alcohol, under acid or base catalysis
C) Amide formation
D) Hydrolysis only

B. Biodiesel production uses transesterification of triglycerides with methanol.

23. (9.12) Thioesters like acetyl-CoA:

A) Are weaker acyl donors than esters
B) Are completely inert
C) Are "activated" acyl donors, with reactivity between anhydrides and esters; central to metabolism
D) Are always cyclic

C. Sulfur's poor π donation makes the thioester carbonyl more electrophilic than an ester.

24. (9.12) Amides are biologically critical because:

A) They are easily hydrolyzed under any condition
B) They decompose spontaneously in water
C) They react with DNA nucleobases
D) Peptide bonds in proteins are amides, and their resistance to hydrolysis gives proteins stability

D. Without amide stability, proteins would hydrolyze spontaneously and life as we know it would be impossible.

Previous Attempts

Carboxylic acid derivatives all share one structural feature: an acyl group (R-CO-) attached to a leaving group. The identity of that leaving group - chloride, carboxylate, alkoxide, or amide nitrogen - sets everything: reactivity, product distribution, and biological role.

This chapter unifies the four main derivatives (acyl halides, anhydrides, esters, amides) under the single reactivity ladder and the nucleophilic acyl substitution mechanism from Chapter 8. Master the ladder, and every derivative reaction follows the same script.

The Central Analogy

💡 Real World

The reactivity ladder = a one-way escalator. Moving from more reactive to less reactive (acyl halide → anhydride → ester → amide) is easy - gravity does the work, and the reaction is spontaneous. Moving up the ladder requires activation energy (like SOCl₂ to regenerate the acid chloride from the acid). Knowing which direction is favored lets you plan multi-step syntheses.

In This Chapter

9.1 Overview - What the Derivatives Share
9.2 Acyl Halides - Structure and Reactivity
9.3 Anhydrides
9.4 Esters - Structure, Formation, Hydrolysis, Transesterification
9.5 Amides - Structure, Resonance, Stability
9.6 Relative Reactivity - Why the Ladder Exists
9.7 Nucleophilic Acyl Substitution - Detailed Mechanism
9.8 Interconversion of Derivatives
9.9 Hydrolysis - Acid vs Base Conditions
9.10 Reactions with Amines - Amide Bond Formation
9.11 Reactions with Alcohols - Ester Formation
9.12 Biological Relevance - Peptide Bonds, Thioesters, Aspirin
Section Test

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