See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: Under acid-catalyzed conditions, a 1,2-diol reacts with an aldehyde (PhCHO) to form a cyclic acetal known as a 1,3-dioxolane. This is a classic protection/condensation reaction of vicinal diols with carbonyl compounds. Step 1 - Identify the reactants: The starting material is a vicinal diol (1,2-diol) where each hydroxyl-bearing carbon also carries a 2-methylcyclopropyl group. PhCHO is benzaldehyde. The conditions are H+ (acid catalyst). Step 2 - Reaction mechanism: Under acid catalysis, the aldehyde is activated (protonated), and the diol acts as a nucleophile. The two OH groups of the 1,2-diol condense with benzaldehyde to form a five-membered cyclic acetal (1,3-dioxolane). One molecule of water is lost. The product is 2-phenyl-4,5-bis(2-methylcyclopropyl)-1,3-dioxolane. Step 3 - Identify product structure: The product has a PhCH bridging two oxygen atoms, which are in turn each connected to one of the original diol carbons (each still bearing its 2-methylcyclopropyl group). This matches option (b): Ph-CH(-O-)(-O-) with the two oxygens forming a five-membered ring with the two carbons bearing 2-methylcyclopropyl groups. Step 4 - Why other options fail: - Option (a): Shows a CH(Ph) directly bonded to the central carbon without oxygens - this would require a C-C bond formation, not the expected acetal chemistry. - Option (c): Shows an epoxide product, which would require loss of water from the diol alone without involvement of PhCHO; PhCHO would not be incorporated. - Option (d): Shows an alkene (dehydration product), which does not incorporate PhCHO and is not the major product under these mild acetal-forming conditions. The 96% yield strongly supports the thermodynamically favorable cyclic acetal formation from a 1,2-diol and an aldehyde under acid catalysis. Therefore, the correct answer is B.