KCET · Chemistry · General Organic Chemistry

Among the following, which is least acidic?

A phenol
B -cresol
C -nitrophenol
D -chlorophenol

Verified Solution

Answer & Solution

Correct Answer

(B) -cresol

Step-by-step Solution

Detailed explanation

When an electron attracting group (like \(-\mathrm{NO}_{2},-\mathrm{Cl}\) ) is attached to the phenol ring, it stabilises the negative charge on the oxygen of phenoxide ion. Due to this reason acidic character of phenol increases. But when an electron donating group (like \(-\mathrm{CH}_{3}\) ) is attached to the phenol ring, it destabilises the ring and hence, acidic character of phenol decreases. Thus, the correct order of acidic character is -nitrophenol > -chlorophenol \(>\) phenol \(>\) -cresol

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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