Name: Use of Carboxylic Acids
Uploaded: 2019-07-19
Duration: 1 min 44 s
Description: Do you know the compound which is used as a food preservative and condiment? Which acid is used in the treatment of bacterial infections? Let's know more thr...

Question

Explain why carboxylic acids behave as acids? Discuss briefly the effect of electron donating and electron withdrawing substituents on the acidity of aliphatic carboxylic acids.

Accepted Answer

Carboxylic acids are weaker acids as compared to mineral acids. The strength of acids depends upon the extent of ionisation which mainly depends upon the stability of the carboxylate ion formed.

(i) A carboxylate acid molecule is a resonance hybrid of the following two hybrid structures.

The structure II indicates that the oxygen atom of the hydroxyl group carries some positive charge. As a result, the electron pair of $O - H$ is drifted towards oxygen atom. This displacement of electron pair causes the formation of proton and carboxylate ion. The carboxylate ion which is formed is also resonance hybrid of the two following structures III and IV.

Thus we observe that,

(i) The contributing structures of carboxylic acids (I and II) are not equivalent and the second structure involves charge separation. As a result, the structure II contributes less stability of the carboxylic acid. The resonating structures III and IV are equivalent and contribute greater stability to carboxylate ion.

Thus, carboxylate ion being more stable than the undissociated carboxylic acid, the latter has a tendency to dissociate into proton and the carboxylate ion. Hence, the carboxylic acid shows acidic character.

The strength of carboxylic acid depends on the nature of electron withdrawing substituent. Greater the power of the substituent, stronger is the acid.For example consider acetic acid and formic acid. Acetic acid has methyl group attached to carboxylic acid group which is electron donating group. The presence of electron donating group reduces the strength of acid. On the other hand, formic acid does not contain such groups. Hence, formic acid is stronger than acetic acid.

Explain why carboxylic acids behave as acids? Discuss briefly the effect of electron donating and electron withdrawing substituents on the acidity of aliphatic carboxylic acids.

Important Questions on Carboxylic Acids

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