See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the starting materials and reaction A: Cyclohexanone reacts with 1,1,1-tris(hydroxymethyl)methane? No — the triol shown is HOCH2CH(OH)CH2OH, which is 1,2,3-propanetriol (glycerol). Under acid-catalyzed conditions (H+), a ketone reacts with a 1,2-diol or 1,3-diol to form a cyclic acetal (ketal). Glycerol has both a 1,2-diol and a 1,3-diol relationship. With cyclohexanone and H+, the thermodynamically and kinetically preferred product is the 5-membered 1,3-dioxolane (using the 1,2-diol portion). The product (A) is 2-(hydroxymethyl)-1,3-dioxaspiro[4.5]decane — i.e., the spiro ketal of cyclohexanone with the 1,2-diol portion of glycerol, leaving one free primary hydroxyl group (-CH2OH) at C-4 of the dioxolane ring. Step 2 - Reaction of (A) with dimethyl sulfate (Me-O-S(=O)(=O)-OMe) and base: Dimethyl sulfate is a methylating agent. The reagent shown is MeO-SO2-OMe (dimethyl sulfate). Under basic conditions, the free hydroxyl group (-CH2OH) on compound (A) undergoes O-methylation (Williamson-type ether synthesis) to give -CH2OMe. The base deprotonates the alcohol, and the alkoxide attacks the electrophilic methyl group of dimethyl sulfate in an SN2 reaction, yielding a methyl ether. Step 3 - Structure of product (B): Product (B) is the spiro ketal (1,3-dioxaspiro[4.5]decane framework) bearing a -CH2OMe group at C-4 of the dioxolane ring. This matches option (b). Step 4 - Why other options fail: (a) Shows a methyl group — this would result from C-methylation or a different substrate, not O-methylation of the hydroxymethyl group. (c) Shows -CH2SO2OMe — this would imply the sulfonate ester remained intact rather than the alcohol being methylated; dimethyl sulfate transfers the methyl group, not the sulfonate moiety. (d) Shows -CH2SO3Me — a sulfonate ester product, which is not formed when dimethyl sulfate acts as a methylating agent under basic conditions. The O-methylation of the primary alcohol in (A) by dimethyl sulfate/base gives the methyl ether -CH2OMe, corresponding to structure (b). Therefore, the correct answer is B.