3. Answer in brief.

i. Why phenol is more acidic than ethyl alcohol ?


Phenol (C6H5OH) is more acidic than ethyl alcohol (C2H5OH) due to differences in their chemical structures. The acidity of a compound is related to its ability to donate a proton (H+) to a base. In the case of phenol and ethyl alcohol, the key difference lies in the nature of the functional groups attached to the hydroxyl group (-OH) in these molecules.

Here’s why phenol is more acidic than ethyl alcohol:

  1. Resonance stabilization: Phenol has a benzene ring (C6H5) attached to the -OH group. This benzene ring can delocalize the negative charge that forms on the oxygen atom after it donates a proton. This resonance stabilization of the negative charge distributes it across the entire ring, making it more stable. In contrast, ethyl alcohol lacks a resonance-stabilizing group.

  2. Electronegativity of the substituent: In phenol, the benzene ring is electron-rich due to the presence of pi bonds in the ring. This electron density helps stabilize the negative charge on the oxygen atom. In ethyl alcohol, the ethyl group (-C2H5) is electron-releasing but not as effective in stabilizing the negative charge as the benzene ring.

  3. Inductive effect: The carbon atoms in the ethyl group are less electronegative than the carbon atoms in the benzene ring. This means that the benzene ring has a greater ability to withdraw electron density from the oxygen atom, making the oxygen atom more willing to donate a proton (H+). In contrast, the ethyl group’s inductive effect is weaker.

As a result of these factors, phenol has a more acidic hydrogen atom attached to the -OH group compared to ethyl alcohol. This increased acidity means that phenol can readily lose a proton to form the phenoxide ion (C6H5O-) in the presence of a base, making it a stronger acid than ethyl alcohol.