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Organic Chemistry · Acyl Derivatives

Nucleophilic Acyl Substitution & Derivatives

Compare acid chlorides, anhydrides, esters and amides using the tetrahedral intermediate.

Illustrated explanationsWorked examplesSelf-checkFree worksheet

1. Understand the Concept

Carboxylic acid derivatives carry a group X on the acyl carbon: R–C(=O)–X. Nucleophilic addition gives a tetrahedral intermediate; reformation of the C=O group expels a suitable leaving group. A useful introductory reactivity trend is acyl chlorides > anhydrides > esters ≈ carboxylic acids > amides, with conditions and leaving-group protonation affecting outcomes.

Learning outcome: Explain why nucleophilic acyl substitution usually replaces a leaving group and predict products for common acid derivatives.

2. Follow a Consistent Strategy

  1. Identify the acyl compound and potential leaving group X.
  2. Identify the nucleophile (water, alcohol or amine) and any acid/base catalyst.
  3. Draw nucleophilic attack followed by a tetrahedral intermediate.
  4. Re-form C=O and remove X; complete proton transfers and account for the byproducts.

3. See the Chemistry

Three-panel Acyl Substitution schematic with structures and concise explanations
Educational schematic with condensed structures; conditions and substituents determine the detailed mechanism.

4. Work Through Examples

Worked example 1

Acid chloride to ester

CH₃COCl + CH₃CH₂OH → CH₃COOCH₂CH₃ + HCl

The alcohol replaces chloride; a base is often added to neutralize the generated acid.

Worked example 2

Ester aminolysis

CH₃COOCH₃ + NH₃ → CH₃CONH₂ + CH₃OH

Under suitable conditions an amide can form; ester aminolysis may require heating or excess nucleophile.

5. Avoid These Mistakes

  • Confusing nucleophilic addition (aldehyde/ketone) with addition–elimination (most acyl derivatives).
  • Assuming amide is the most reactive derivative because nitrogen is strongly basic; amides are resonance-stabilized and comparatively unreactive.
  • Assuming every nucleophilic acyl substitution proceeds rapidly under room-temperature neutral conditions.

6. Review & Check Understanding

What happens after attack on an acyl derivative?

The tetrahedral intermediate collapses, restoring C=O and expelling an appropriate leaving group.

Which is generally more reactive to substitution, acetyl chloride or acetamide?

Acetyl chloride, which has a better leaving group and less amide-type resonance stabilization.

7. Test Your Understanding

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INTERACTIVE CHEMISTRY PRACTICE

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