Target Exam

CUET

Subject

Chemistry

Chapter

Organic: Aldehydes, Ketones and Carboxylic Acids

Question:

Read the passage carefully and answer the Questions.

Carboxylic acids are the earliest organic compounds isolated from nature. These are also known as organic acids but are weaker acids as compared to mineral acids. However, they are more acidic than alcohols and phenols because of greater resonance stabilization of the parent acid and its conjugate base. The acidic strength is determined by the Ka, which is called the acidity constant. The greater the value of Ka, the greater the tendency of the acid to ionize and hence the stronger the acid. The acidic strength of the saturated aliphatic carboxylic acid depends upon the inductive effect and its position with respect to - COOH groups. Electron-donating substituents tend to decrease whereas electron -withdrawing substituents tend to increase the acidic strength. The acidic strength of the aromatic carboxylic acid, on the other hand depends upon both the inductive effect and the resonance effect of the substituents.

p-Nitrobenzoic acid is a stronger acid than benzoic acid because of

Options:

-R and -I effect of nitro group

Only -R effect of Nitro group

Only -I effect of Nitrogroup

+R effect and -I effect of nitro group

Correct Answer:

-R and -I effect of nitro group

Explanation:

The correct answer is Option (1) → -R and -I effect of nitro group **

p-Nitrobenzoic acid has a nitro group (–NO₂) at the para position.

The –I (inductive) effect withdraws electron density through the sigma bond, stabilizing the conjugate base.

The –R (resonance) effect delocalizes the negative charge of the carboxylate ion onto the nitro group via resonance.

Both effects increase the acidity compared to benzoic acid.