See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: Electrophilic addition of Br2 to an alkene follows an anti-addition mechanism via a bromonium ion intermediate. The two bromine atoms add across the double bond in a vicinal (1,2) fashion. Step 1: Identify the substrate. 1-Butene is CH2=CH-CH2-CH3 (double bond between C1 and C2). Step 2: Mechanism of Br2 addition. Br2 acts as an electrophile; it forms a cyclic bromonium ion intermediate across the C1=C2 double bond. A bromide ion then attacks from the back side (anti addition), placing one Br on C1 and one Br on C2. Step 3: Product identification. The product is 1,2-dibromobutane: BrCH2-CHBr-CH2-CH3. One Br on C1 and one Br on C2 of a four-carbon chain. Step 4: Evaluate options. - Option (a): Shows a geminal dibromide (both Br on same carbon, C1), i.e., 1,1-dibromobutane. This would result from addition of HBr twice or from a different mechanism, not from Br2 addition to 1-butene. Incorrect. - Option (b): Shows Br atoms on a branched (2-methyl) framework inconsistent with 1-butene (a straight-chain alkene). Incorrect. - Option (c): Shows 1,4-dibromobutane (Br on C1 and C4). This is not a vicinal addition product; it would require a radical or different mechanism placing Br at opposite ends. Incorrect. - Option (d): Shows 1,2-dibromobutane with Br on C1 and Br on C2 of a straight four-carbon chain. This is exactly the vicinal dibromide expected from anti addition of Br2 to 1-butene. Correct. Therefore, the correct answer is D.