See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: To synthesize hexanal (a 6-carbon aldehyde, CH3CH2CH2CH2CH2CHO), we need a reliable method that builds the correct carbon skeleton and installs an aldehyde at the terminal position. Step-by-step analysis of option D: Step 1: CH3CH2CH2CH2MgBr (butylmagnesium bromide, a Grignard reagent) reacts with ethylene oxide (H2C-CH2 with an O bridge, i.e., oxirane). Grignard reagents open epoxides via nucleophilic attack at the less hindered carbon. Butyl Grignard attacks the terminal carbon of ethylene oxide, adding two carbons and yielding, after workup, a primary alcohol: CH3CH2CH2CH2CH2CH2OH (1-hexanol) — wait, that is a 6-carbon primary alcohol. Step 2: H3O+ workup protonates the alkoxide to give 1-hexanol (CH3CH2CH2CH2CH2CH2OH), a primary alcohol with 6 carbons. Step 3: PCC (pyridinium chlorochromate) in CH2Cl2 oxidizes a primary alcohol to an aldehyde (but not further to a carboxylic acid). 1-hexanol is oxidized to hexanal (CH3CH2CH2CH2CH2CHO). This sequence cleanly gives hexanal in 3 steps with correct carbon count and functional group. Why other options fail: - Option (a): CH3CH2CH2CH2Br + NaC≡CH gives a terminal alkyne (1-hexyne, 6 carbons). Markovnikov hydration with H2SO4/HgSO4 of a terminal alkyne gives a methyl ketone (2-hexanone), NOT hexanal. This gives the wrong product. - Option (b): Epoxidation of 1-pentene with peracid gives 1,2-epoxypentane (5 carbons). CH3MgBr opens the epoxide to give a 6-carbon secondary alcohol (2-hexanol after H3O+ workup), and PCC oxidation would give 2-hexanone, not hexanal. Wrong regiochemistry. - Option (c): Starting with 2-hexanone, Baeyer-Villiger oxidation with peracid inserts oxygen to give a 6-carbon ester (hexanoate ester), LiAlH4 reduction of the ester gives a primary alcohol (1-hexanol or mixture), PCC oxidation gives hexanal — this sequence is longer (5 steps) and less efficient/clean compared to option D. Additionally, Baeyer-Villiger on a methyl ketone preferentially migrates the larger group, so the product would be pentyl formate or methyl pentanoate depending on migration, making the carbon count and product less straightforward. This is not the best synthesis. Option D is the most direct, efficient, and reliable synthesis of hexanal. Therefore, the correct answer is D.