Structure, functional derivatives and acidity of carboxylic group

Carboxylic Acids

Contents

• Carboxyl group

• Functional derivatives of carboxylic acids

• Acidity of carboxylic acid

Learning
Objectives

At the end of this
lecture, student will be able to

• Identify structure of carboxyl group

• Explain functional derivatives of carboxylic acid

• Explain acidity of carboxylic acids

Carboxylic
Acids

• Carboxyl group → carbonyl group + hydroxyl group

• Functional
derivatives of carboxylic acids

 

• Functional
derivatives of carboxylic acids

Amide

Acid anhydrides

Ionisation
of Carboxylic Acids

• Carboxylic acids in solution dissociate into carboxylate
ion

• Ka – acidity constant

• Larger the ka → greater the ionization → stronger the acid

Acidity of
Carboxylic Acids

• Carboxylic acids – more acidic than corresponding alcohols

• Example

• Resonance effect


Resonance stabilised acetate ion

• Equivalent resonance structures for acetate ion

• Greater resonance stabilization

• Reduces energy for ionisation

No resonance
stabilization for alcohol and alkoxide ion

• Carboxylic acid yields resonance-stabilized anion,
stronger acid than alcohol

Inductive effect

• Inductive effect of carbonyl group – responsible for
acidity of carboxylic acids

• In both compounds – O—H bond – highly polarized by greater
electronegativity of the oxygen atom

• Carbonyl group – more powerful electron attracting inductive
effect than CH2 group

• Large resonance stabilization of carboxylate ion

• Acidity of a carboxylic acid – due to powerful resonance
stabilization of its anion

• Stabilization and the resulting acidity possible because
of the presence of the carbonyl group

Summary

• Carboxyl group – carbonyl and hydroxyl group

• Functional derivatives of carboxylic acid – acid halide,
ester, amide, acid anhydride

• Acidity of carboxylic acid – acidity constant Ka

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