Ch. 20 - Carboxylic Acid Derivatives: NAS See 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
Johnny Betancourt

An ester is one of many moieties in organic chemistry and consists of a carbonyl with an alkoxy group directly attached to the carbonyl carbon.

Structure and electron distribution

Here’s the Lewis structure of an ester, specifically methyl ethanoate. On the left, the green numbers show the electronegativity values of carbon (2.5) and oxygen (3.5). On the right, we have the partial charges that help explain the reactions below. 

Lewis structure and dipolesLewis structure and dipoles

The general formula of an ester is RCOOR, and you can replace the CH3 groups above with R to visualize the proper connection or linkage. 

Ester vs ether

Students often confuse esters and ethers, so let’s take a look at the difference between their structures:

Ester and etherEster and ether

Generally, the properties of esters and ethers are pretty different. For example, ethers are stable under basic conditions but esters are not. 

Reactions

Fischer esterification

The Fischer esterification is a great way to make an ester from a carboxylic acid. It is a reversible reaction between a carboxylic acid, an alcohol, and a Bronsted acid catalyst. Let’s take a look at the mechanism below: 

Fischer esterification mechanismFischer esterification mechanism

The protonation of the carbonyl oxygen creates a very electrophilic carbon because of resonance, and the nucleophilic oxygen of the alcohol attacks it. The catalytic acid makes it easier to attack the carbonyl and promotes nucleophilic acyl substitution

Protonated carbonyl resonanceProtonated carbonyl resonance

Transesterification

Let’s say we want to convert methyl ethanoate to ethyl ethanoate (learn ester nomenclature here). How can we accomplish this transformation? It’s just a question of using the right nucleophile! We can use the same acid catalyst and just use ethanol as the alcohol. The ethanol will replace the methoxy group as the alkoxy group. 


Transesterification with H2SO4Transesterification with H2SO4

Hydrolysis of ester  

Acidic hydrolysisAcidic hydrolysis

Saponification 

If we use hydroxide on an ester, we’ll end up with a carboxylate. If a carboxylic acid is desired, an acid is added to the solution after the carboxylate has been made. In this reaction, we used sulfuric acid in the last step. 

RCOOR to RCOOH with baseRCOOR to RCOOH with base

Saponification is actually how soap is made! You treat a triglyceride with lye (hydroxide) get a carboxylate (the soap) and glycerol.

Basically, there are two ways to go from an ester to a carboxylic acid! Base or acid can be used, but the basic conditions of saponification require an extra step to result in the hydroxyl group! 


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.