See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the functional group present in the structure: The molecule shown is a six-membered cyclic structure (tetrahydropyran ring) where the ring oxygen is at the top. The carbon directly bonded to this ring oxygen (the anomeric carbon, C2) carries both an -OH group and an -H atom. Step 2 - Apply the definition of a hemiacetal: A hemiacetal is formed when one equivalent of an alcohol adds to an aldehyde (or ketone). It has the general structure R-CH(OH)-OR', where one oxygen is part of an -OH group and the other oxygen is an ether-type oxygen. In cyclic form, a hemiacetal arises from intramolecular cyclization of a hydroxy-aldehyde: the hydroxyl oxygen becomes the ring ether oxygen, and the former carbonyl carbon now bears both -OH and -H (from the original aldehyde hydrogen), fitting exactly the structure shown. Step 3 - Confirm the structural match: The shown structure has: - An ether oxygen in the ring (one O bonded to two carbons) - The carbon at the ring-oxygen junction bearing -OH and -H This is precisely the cyclic hemiacetal pattern: C bonded to -OR (ring O), -OH, -H, and one more carbon. Step 4 - Eliminate other options: (a) Acetal: An acetal has two -OR groups on the same carbon (R-CH(OR')2), no free -OH. The structure has only one ether oxygen (in the ring) plus a free -OH, so it is NOT an acetal. (c) Hydrate (gem-diol): A hydrate has two -OH groups on the same carbon (R-CH(OH)2). The structure has one -OH and one ether oxygen, not two -OH groups. (d) Cyanohydrin: A cyanohydrin has an -OH and a -CN on the same carbon. No nitrile group is present. Therefore, the correct answer is B.