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Ch. 20 - Carboxylic Acid Derivatives: NAS WorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins
Ch. 26 - Transition Metals
Carboxylic Acid Derivatives
Naming Carboxylic Acids
Diacid Nomenclature
Naming Esters
Naming Nitriles
Acid Chloride Nomenclature
Naming Anhydrides
Naming Amides
Nucleophilic Acyl Substitution
Carboxylic Acid to Acid Chloride
Fischer Esterification
Acid-Catalyzed Ester Hydrolysis
Lactones, Lactams and Cyclization Reactions
Decarboxylation Mechanism
Additional Guides
Carboxylic Acid
Johnny Betancourt

Fischer Esterification is an acid-catalyzed method to turn carboxylic acids into esters through nucleophilic acyl substitution.

General Reaction:

Fischer esterification (aka Fischer-Speier esterification and acid-catalyzed esterification) is a great way to take a carboxylic acid and convert it into an ester. All that’s required is a carboxylic acid, a strong acid catalyst, and an alcohol. Let’s go ahead and use acetic acid, H3O(same as writing H+), and ethanol to demonstrate the mechanism. To be clear, any acid like H2SO4 or HCl works just fine; we’re just going to use protonated water here.


Starting material reagents and productStarting material, reagents, and product

The first step of this reaction is the protonation of the carbonyl oxygen to form an electrophilic carbon. Either resonance form can be used for the rest of the mechanism.

nucleophilic attackNucleophilic attack

The alcohol then comes in and attacks the carbon to form a tetrahedral intermediate.

Proton transferProton transfer

Next an intramolecular proton transfer occurs to form a hydronium ion.

reform-the-carbonylReform the carbonyl

Once that happens, the carbonyl is reformed and water is kicked off.


All that’s left to do is deprotonate the carbonyl.

Now that you've learned about Fischer esterification, you know the game plan for nucleophilic acyl substitution (NAS). NAS can be used to make tons of molecules like benzoic acid and aspirin!


Notice that we ended up with our acid again? That’s why this is considered an acid-catalyzed mechanism. Of course, there’s also base-catalyzed esterification. Be sure to check out my lesson dedicated to carboxylic acid derivatives. Good luck studying!

Johnny Betancourt

Johnny got his start tutoring Organic in 2006 when he was a Teaching Assistant. He graduated in Chemistry from FIU and finished up his UF Doctor of Pharmacy last year. He now enjoys helping thousands of students crush mechanisms, while moonlighting as a clinical pharmacist on weekends.