Question

In which of the following, intramolecular hydrogen bonding is present?

• A. Resorcinol
• B. Catechol
• C. Quinol
• D. o-Cresol

Hint:

For intramolecular H-bonding to occur in substituted benzene rings, the two participating groups must be in the ortho (1,2) position to each other. Groups in meta (1,3) or para (1,4) positions are too far apart. Common examples include catechol, o-nitrophenol, and salicylaldehyde.

Answer 1

The Correct Option is B

Step 1: Understanding Intramolecular Hydrogen Bonding: Intramolecular hydrogen bonding occurs when a hydrogen atom bonded to an electronegative atom (like O, N, F) forms a bond with another electronegative atom within the same molecule. This typically requires the two groups to be in close proximity (e.g., ortho position in benzene derivatives).
Step 2: Analyzing the Structures:
Resorcinol: Benzene-1,3-diol. The -OH groups are at meta positions (1,3). They are too far apart for effective intramolecular H-bonding. They form intermolecular H-bonds.
Catechol: Benzene-1,2-diol. The -OH groups are at ortho positions (1,2). They are adjacent to each other, allowing the H of one -OH group to form a hydrogen bond with the O of the adjacent -OH group. This is intramolecular hydrogen bonding.
Quinol (Hydroquinone): Benzene-1,4-diol. The -OH groups are at para positions (1,4). They are far apart, leading to intermolecular H-bonding.
o-Cresol: 2-Methylphenol. Contains one -OH and one -CH$_3$ group. Since -CH$_3$ does not have an electronegative atom with a lone pair capable of accepting a hydrogen bond effectively in this context (C is not electronegative enough), significant H-bonding doesn't occur.

Step 3: Conclusion: Catechol exhibits intramolecular hydrogen bonding due to the proximity of the two hydroxyl groups.