JEE Chemistry 2023 Question with Solution

Given: The acidity order of hydroxyl compounds A, B, C, D and E is to be compared.

Find: The correct decreasing order of acidity.

Acidity of a compound is related to the stability of its conjugate base. The more stabilized the conjugate base, the stronger the acid.

• E $(\text{NO}_2\text{-group})$: The $\text{NO}_2$ group is electron-withdrawing and stabilizes the conjugate base, increasing the acidity.
• C (Phenol): This has no electron-donating or electron-withdrawing group, so it has moderate acidity.
• D (Methoxy group, $\text{OCH}_3$): The methoxy group is electron-donating and reduces the acidity by destabilizing the conjugate base.
• A (Methanol): Alcohols generally have low acidity compared to phenols due to the absence of a conjugate base that can be stabilized by resonance.
• B (Tertiary alcohol): The tertiary alcohol, due to steric hindrance and electron-donating alkyl groups, is the least acidic.

Thus, the correct order of acidity is

$$\text{E} > \text{C} > \text{D} > \text{A} > \text{B}$$

Therefore, the correct option is A. The solution shows D, but the worked conclusion matches option A.

Given: Substituted phenols and alcohols are to be arranged in order of acidity.

Find: Which option matches the correct order.

The key idea is conjugate base stabilization:

1. Phenoxide ions are more stable than simple alkoxide ions because the negative charge can be delocalized by resonance.
2. An electron-withdrawing group further stabilizes the phenoxide ion and increases acidity.
3. An electron-donating group destabilizes the phenoxide ion and decreases acidity.
4. Among ordinary alcohols, tertiary alcohol is less acidic than methanol because alkyl groups donate electron density and reduce stability of the conjugate base.

So,

$$\text{nitro substituted phenol} > \text{phenol} > \text{methoxy substituted phenol} > \text{methanol} > \text{tert-butanol}$$

which corresponds to

$$\text{E} > \text{C} > \text{D} > \text{A} > \text{B}$$

Hence, the correct option is A.