See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Step 1 - Understand the reaction sequence: X undergoes (1) NaOH, (2) Heat, (3) H2/Pd, (4) LiAlH4 then H2O to give the final product. Step 2 - Work backwards from the product. The final step is LiAlH4 followed by H2O, which reduces a carbonyl group (aldehyde or ketone or ester) to an alcohol. Since the product is a primary alcohol (terminal -CH2OH), the precursor before LiAlH4 must be an aldehyde (terminal -CHO). Step 3 - The step before LiAlH4 reduction is H2/Pd (catalytic hydrogenation), which reduces a C=C double bond to a C-C single bond. So before hydrogenation, there was an alpha,beta-unsaturated aldehyde (enal) with a C=C adjacent to the CHO. Step 4 - The step before hydrogenation is Heat (elimination/condensation). The step before that is NaOH. The combination of NaOH then Heat suggests an aldol condensation followed by dehydration, giving an alpha,beta-unsaturated carbonyl compound (aldol dehydration product = enal). Step 5 - Working back: after aldol condensation and dehydration we get an alpha,beta-unsaturated aldehyde. After H2/Pd we get a saturated aldehyde. After LiAlH4/H2O we get the primary alcohol (the product shown). Step 6 - The product primary alcohol corresponds to: if we convert -CH2OH back to -CHO, we get a saturated aldehyde. The product structure (analyzing the image) corresponds to 4-methylhexan-1-ol when the CH2OH is considered, meaning the saturated aldehyde precursor is 4-methylhexanal. Step 7 - The alpha,beta-unsaturated aldehyde (enal) before H2/Pd would be 4-methylhex-2-enal (with the double bond between C2 and C3, conjugated with the aldehyde at C1). Step 8 - This enal is formed by aldol condensation and dehydration (NaOH, then Heat) of compound X. An alpha,beta-unsaturated aldehyde formed from aldol dehydration of a single aldehyde with itself (self-aldol) or crossed aldol. For 4-methylhexanal to form via reduction of the enal, and the enal to form from NaOH + heat of X, compound X must be the simple aldehyde: 4-methylhexanal (option d), which undergoes self-aldol condensation (NaOH) to give a beta-hydroxy aldehyde, then dehydration (heat) to give the alpha,beta-unsaturated aldehyde (2-(2-methylbutyl)but-2-enal or similar enal), then hydrogenation and reduction gives the observed product. Step 9 - Confirming option d: O=CH-CH2CH2CH(CH3)CH2CH3 is 4-methylhexanal. NaOH causes aldol condensation (self-condensation), heat causes dehydration to enal, H2/Pd reduces the C=C giving saturated aldehyde, LiAlH4/H2O reduces CHO to CH2OH giving the branched primary alcohol shown. Step 10 - Why other options fail: (a) and (b) are already alcohols - they would not undergo NaOH/Heat/H2/Pd sequence to give the product. (c) is a longer-chain aldehyde (5-methylheptanal) that would give a different product with extra carbons not matching the shown product. Only (d) 4-methylhexanal fits the retrosynthetic analysis. Therefore, the correct answer is D.