See image — Alcohols Phenols and Ethers Chemistry Question

💡 Solution & Explanation

Concept: Acid hydrolysis of a cyclic acetal (or mixed acetal) proceeds via stepwise protonation and loss of the alkoxy groups to regenerate the carbonyl compound (aldehyde or ketone) and the alcohols. Step 1: Identify the starting material. The starting material is a cyclic acetal derived from tetrahydropyran-2-ol framework. Specifically, it is 2-(RCH2-O-methyl) tetrahydropyranyl acetal — more precisely, it is the acetal of 5-hydroxypentanal with RCH2OH (i.e., the intramolecular hemiacetal of 5-hydroxypentanal cyclized and then etherified with RCH2OH). The structure shown is a tetrahydropyran ring (six-membered ring with one oxygen) bearing an -O-CH2R group at C2, making it a mixed acetal: C2 is bonded to both the ring oxygen and the exocyclic -O-CH2R. Step 2: Acid hydrolysis of an acetal. Under H3O+ conditions, acetals are hydrolyzed. The acetal carbon (C2 of the ring) is protonated on one oxygen, and the better leaving group (RCH2OH, the exocyclic alkoxy group) leaves first to give an oxocarbenium ion (endocyclic). Then water attacks or the ring oxygen assists. Full hydrolysis of the acetal would regenerate the open-chain hydroxy aldehyde. Step 3: The cyclic acetal here is specifically the acetal formed from 5-hydroxypentanal cyclizing to give a hemiacetal (tetrahydropyranyl hemiacetal) and then reacting with RCH2OH to give the full acetal. Acid hydrolysis reverses this: the exocyclic -OCH2R is cleaved first (since the endocyclic oxygen stabilizes the oxocarbenium better), releasing RCH2OH and generating the cyclic hemiacetal intermediate, which then opens under acidic aqueous conditions to give the open-chain 5-hydroxypentanal (HO-(CH2)4-CHO). Step 4: The products are 5-hydroxypentanal (an omega-hydroxy aldehyde) and RCH2OH, which matches option (c): structure showing HO and CHO on a five-carbon chain + RCH2OH. Why other options fail: - (a) Dihydropyran + RCH2OH: This would require elimination, not simple hydrolysis under mild acid conditions. - (b) Hemiacetal retaining -OCH2R: This is only partial hydrolysis giving a hemiacetal, not the major product under aqueous H3O+ where full hydrolysis to the hydroxy aldehyde is favored. - (d) A diol acetal-opened product: This does not correctly represent the hydrolysis pathway of a simple acetal. Therefore, the correct answer is C.