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Chapter 3: Problem 149

Which among the following is more acidic than phenol? (a) o-methoxy phenol (b) \(\mathrm{m}\) -methoxy phenol (c) p-methoxyphenol (d) none of these

Short Answer

Expert verified
Answer: (c) p-methoxy phenol is more acidic than phenol.

Step by step solution

01

Understand the acidity of phenol

Phenol is an acidic compound because of its ability to lose a hydrogen ion (proton) from the hydroxyl group (-OH). The resulting conjugate base, called phenoxide ion, is resonance stabilized and this stability increases the acidity of phenol.
02

Analyze the effect of methoxy group on phenol acidity

The methoxy group (-OCH\(_{3}\)) is an electron-donating group, meaning it increases the electron density in the molecule by donating electrons through resonance or inductive effect. The position of the methoxy group on the phenol molecule will play a significant role in its acidity.
03

Compare the acidity of o-methoxy phenol (a)

In o-methoxy phenol, the methoxy group is present at the ortho position, i.e., adjacent to the hydroxyl group. The electron-donating effect of the methoxy group destabilizes the phenoxide ion formed after the removal of the proton. Thus, o-methoxy phenol is less acidic than phenol.
04

Compare the acidity of m-methoxy phenol (b)

In m-methoxy phenol, the methoxy group is present at the meta position. The electron-donating effect in this case is weaker than the ortho position due to the lesser extent of resonance in the phenoxide ion. However, it is still weaker than the original phenol molecule, and this makes m-methoxy phenol less acidic than phenol as well.
05

Compare the acidity of p-methoxy phenol (c)

In p-methoxy phenol, the methoxy group is present at the para position. In this case, the methoxy group is not directly conjugated with the phenol ring (-OH), and the electron-donating effect due to resonance is not significant. Therefore, p-methoxy phenol is more acidic than phenol.
06

Conclusion

Among the given options, p-methoxy phenol (c) is more acidic than phenol. Therefore, the correct answer is (c) p-methoxy phenol.

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Most popular questions from this chapter

When phenol is exposed to air for a long period or treated with chromic acid, it is oxidized to (a) p-benzoquinone (b) glyoxal (c) \(\mathrm{CO}_{2}\) (d) oxalic acid

Statement 1 Nitrobenzene and aniline do not undergo Friedel-Crafts reaction with \(\mathrm{CH}_{3}-\mathrm{CH}_{2} \mathrm{Cl} / \mathrm{AlCl}_{3}\) and Statement 2 \(-\mathrm{NO}_{2}\) and \(-\mathrm{NH}_{2}\) groups combine with \(\mathrm{AlCl}_{3}\) to form adducts.

o-Nitrophenol has lower \(\mathrm{pK}\) than (a) p-nitrophenol (b) o-cresol (c) o-fluorophenol (d) \(\mathrm{p}\) -methoxyphenol

Column I Column II (a) Electrophilic substitution (p) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{~N}_{2} \mathrm{Cl}+\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH} \stackrel{\mathrm{NaOH}}{\longrightarrow}\) (b) Nucleophilic substitution (q) Toluene + \(\mathrm{NBS} \longrightarrow\) (c) Free radical substitution (r) Dow's process (d) Coupling reaction (s) Phenol \(\longrightarrow\) picric acid (t) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{O} \mathrm{Na}+\mathrm{CH}_{3} \mathrm{Br} \longrightarrow\)

The increasing order of acidic strength among p-methoxyphenol, p-cresol and p-nitrophenol is (a) p-cresol \(<\) p-methoxyphenol \(<\) p-nitrophenol (b) p-methoxyphenol \(<\) p-cresol \(<\) p-nitrophenol (c) \(\mathrm{p}\) -cresol \(<\mathrm{p}\) -nitrophenol \(<\mathrm{p}\) -methoxyphenol (d) p-methoxyphenol \(<\) p-nitrophenol \(<\mathrm{p}\) -cresol
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