Chemistry - Carbonyl compounds Question with Solution | TestHub
Which of the following(s) will form stable hemiketal :
Options:(select one or more)
Answer:
Solution:
Question Explanation:
Identifying compounds that form stable cyclic hemiacetals or hemiketals due to favorable ring size. Concept:
Stable Hemiketal Formation and Cyclization.
Solution:
A hemiketal forms when a free hydroxyl in the same molecule attacks a ketone and the resulting O–C bond closes to give a cyclic hemiacetal-type structure. Two factors make the intramolecular hemiketal stable: a free OH is present, and the OH and C=O are spaced so that closure gives a 5- or 6-membered ring (these rings are thermodynamically favoured).
Option (2) HO–(CH2)3–CO–CH3 — the OH at C-1 can attack the ketone carbon (C-4) to give a 5- membered ring hemiketal. This geometry is ideal, so a stable hemiketal is formed.
Option (3) is a polyhydroxy chain around a carbonyl (sugar-like motif). Such substrates readily cyclise to give stable cyclic hemiketals .
Option (1) diphenyl ketone has no OH group — no hemiketal .
Option (4) contains an ether (–O–), not a free OH, so it cannot form a hemiketal intramolecularly.
