See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Concept: Grignard reagents add to carbonyl compounds (ketones and aldehydes) to give tertiary or secondary alcohols. The product of a Grignard reaction is determined by the combination of the carbonyl fragment and the carbanion fragment — specifically, the two carbon groups on the carbonyl carbon plus the Grignard carbon all end up on the same carbon (the new C-OH carbon). Step 1 — Identify the product of reaction (i): The ketone in (i) has a cyclopropyl group and a (2-methylallyl / prenyl-type: CH2-CH=CMe) group both attached to the carbonyl carbon. MeMgX adds a methyl group to the carbonyl. Product: a tertiary alcohol with substituents — cyclopropyl, CH2CH=C(CH3) (the prenyl-type chain), and CH3 — all on the carbinol carbon. Step 2 — Identify the product of reaction (ii): The aldehyde in (ii) has the structure (CH3)2C=CH-CH2-CH2-CHO (a geranial/citronellal-type aldehyde; the chain from CHO is -CH2CH2-CH=C(CH3)2 or similar). The Grignard is cyclopropyl-MgX. Addition of cyclopropyl carbanion to the aldehyde carbon gives a secondary alcohol: HO-CH(cyclopropyl)-(CH2CH2CH=CMe2) chain — but wait, we must check whether the products of (i) and (ii) match. Step 3 — Identify the product of reaction (iii): Cyclopropyl methyl ketone reacts with (CH3)2C=CH-CH2CH2-MgBr. The Grignard adds to the ketone carbonyl. Product: tertiary alcohol with cyclopropyl, CH3, and -CH2CH2-CH=C(CH3)2 all on the carbinol carbon. Step 4 — Compare products: Reaction (i): carbonyl carbon had cyclopropyl + prenyl-type (CH2CH=CMe or CH2CH2CH=CMe2) groups; MeMgX adds CH3 → tertiary alcohol: cyclopropyl, CH3, and the alkenyl chain on C-OH. Reaction (iii): cyclopropyl methyl ketone (cyclopropyl + CH3 on carbonyl) + alkenyl Grignard (CH2CH2CH=CMe2) → tertiary alcohol: cyclopropyl, CH3, and alkenyl chain on C-OH. These are the same tertiary alcohol product — the carbinol carbon bears cyclopropyl, methyl, and the geranyl/prenyl chain in both cases. Reaction (ii) gives a secondary alcohol (from an aldehyde), so its product differs from (i) and (iii). Step 5 — Which reactions give the same product: Reactions (i) and (iii) give the same tertiary alcohol. This corresponds to option D (reactions i and iii). Why (ii) fails: (ii) involves an aldehyde giving a secondary alcohol, structurally different from the tertiary alcohol from (i) and (iii). Therefore, the correct answer is D.