Question

Which of the following compounds shows acidic character?

• A. Phenol
• B. Ethanol
• C. Ether
• D. Ethene

Hint:

To quickly compare the acidity of organic compounds, look for resonance.
The phenoxide ion is stabilized by resonance, whereas alkoxide ions are destabilized by the \(+I\) effect of alkyl groups.
This makes phenols significantly more acidic than aliphatic alcohols like ethanol.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The objective of this question is to identify which of the given organic compounds exhibits a significant acidic character in comparison to the others.

Step 2: Key Formula or Approach:
The acidic strength of an organic compound is directly proportional to the stability of the conjugate base formed after losing a proton (\(H^+\)).
\[ \text{Acidic Strength} \propto \text{Stability of Conjugate Base} \]

Step 3: Detailed Explanation:

• Conjugate Base of Phenol: When phenol (\(C_6H_5OH\)) loses a proton, it forms the phenoxide ion (\(C_6H_5O^-\)).
  
• Resonance Stabilization: The negative charge on the oxygen atom of the phenoxide ion is delocalized over the ortho and para positions of the aromatic benzene ring.
  
• Effect of Resonance: This resonance delocalization stabilizes the phenoxide ion, making the starting phenol relatively eager to release its proton.
  
• Conjugate Base of Ethanol: Deprotonation of ethanol (\(C_2H_5OH\)) yields the ethoxide ion (\(C_2H_5O^-\)).
  
• Inductive Destabilization: The ethyl group in the ethoxide ion exerts a \(+I\) inductive effect, which pushes electron density toward the already negatively charged oxygen, destabilizing the conjugate base.
  
• Acidity of Ether and Ethene: Ether lacks a polar \(O-H\) bond and cannot easily release a proton.
  
• Acidity of Ethene: Ethene (\(C_2H_4\)) contains \(sp^2\) hybridized carbon atoms with low electronegativity, resulting in negligible acidity.
  

Step 4: Final Answer:
Therefore, phenol is the most acidic compound among the choices, which matches option (A).