Select the compound from the following that will show intramolecular hydrogen bonding.

Solution

Chemistry ma’am · 3 steps

Intramolecular means donor and acceptor in the same molecule, close enough to close a ring. Look for that.

1. What it needs. Intramolecular hydrogen bonding needs an O–H or N–H group and an electronegative acceptor (O, N or F) inside the same molecule. They must sit close enough to close a five- or six-membered ring.
2. Option (a). Option (a) is o-nitrophenol. The –OH and the -NO₂ groups are on neighbouring ring carbons. The H of –OH bonds to an O of -NO₂ and closes a stable six-membered ring (a chelate).

   Compound	Donor and acceptor in one molecule, close together?	Type of H-bonding
   (a) o-nitrophenol	Yes: –OH next to -NO₂	intramolecular
   (b) H₂O	No: only one O atom	intermolecular
   (c) C₂H₅OH	No: only one O atom	intermolecular
   (d) NH₃	No: only one N atom	intermolecular

3. So. Only o-nitrophenol can hydrogen-bond within itself, so the answer is (a). Water, ethanol and ammonia each have a single electronegative atom, so they can only H-bond to a neighbouring molecule.

The idea to keep. For intramolecular H-bonding, find a donor and an acceptor in the same molecule that can close a five- or six-membered ring. Ortho-substituted phenols are the classic case.

Answer from the NTA final answer key. Solution by PrepWiser.