Phe­nol is less acidic than:

• A. o−nitrophenol
• B. p−methoxy phenol
• C. 2−methylpropanol
• D. 2, 2−dimethyl pentanol

Phe­nol is a compound that exhibits acidic properties due to the presence of its hydroxyl (-OH) group attached to a benzene ring. When comparing the acidity of phenol to other compounds, we need to consider how substituents on the benzene ring or the structure of the alcohols can influence acidity. Let's break down the options provided to determine which compound is less acidic than phenol.

Understanding Acidity in Organic Compounds

Acidity in organic compounds is often influenced by the stability of the conjugate base formed after deprotonation. For phenol, when it loses a hydrogen ion (H⁺), it forms the phenoxide ion, which is stabilized by resonance. This resonance allows the negative charge to be delocalized over the aromatic ring, enhancing the stability of the conjugate base and thus increasing the acidity of phenol.

Analyzing the Options

• A. o−nitrophenol: The nitro group (-NO₂) is a strong electron-withdrawing group. Its presence at the ortho position increases the acidity of o-nitrophenol compared to phenol because it stabilizes the phenoxide ion through resonance and inductive effects.
• B. p−methoxy phenol: The methoxy group (-OCH₃) is an electron-donating group. This decreases the acidity of p-methoxy phenol compared to phenol because it destabilizes the phenoxide ion by increasing electron density on the ring.
• C. 2−methylpropanol: This is a simple alcohol with a branched structure. It is less acidic than phenol because it does not benefit from resonance stabilization of its conjugate base.
• D. 2, 2−dimethyl pentanol: Similar to 2-methylpropanol, this compound is also an alcohol and is less acidic than phenol for the same reasons.

Comparative Acidity

Now, let's summarize the acidity of each compound:

• o−nitrophenol > phenol (more acidic due to the electron-withdrawing nitro group)
• p−methoxy phenol < phenol (less acidic due to the electron-donating methoxy group)
• 2−methylpropanol < phenol (less acidic, no resonance stabilization)
• 2, 2−dimethyl pentanol < phenol (less acidic, similar reasoning)

Final Thoughts

Among the options, both 2−methylpropanol and 2, 2−dimethyl pentanol are less acidic than phenol. However, if we are to choose one that is distinctly less acidic, we can confidently say that both alcohols (C and D) are less acidic than phenol. If the question asks for just one answer, either C or D would suffice, but they are both valid in this context.

In conclusion, phenol is less acidic than both 2−methylpropanol and 2, 2−dimethyl pentanol, but o−nitrophenol is more acidic, and p−methoxy phenol is less acidic than phenol itself. Thus, the correct answer to your question is that phenol is less acidic than both C and D.