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In the following reaction sequence, identify the correct statements about the unknown compounds: Cyclopropane on heating (delta) gives compound [A]. [A] + HBr / CCl4 gives compound [B]. [B] + Br2 / CCl4 gives compound [C]. [C] -> C2H5CH2CH3 (butane) on reduction with a suitable reagent. Which of the following statements are correct?

1. Compound [B] is cyclopropyl bromide
2. Compound [A] is propene (CH2=CH-CH3)
3. Compound [B] is 1,3-dibromopropane
4. Compound [C] is 1,2,3-tribromopropane

Correct answer: Compound [A] is propene (CH2=CH-CH3)

Solution

If starting material is cyclobutane: heating gives butene (ring opening/isomerization). Butene + HBr gives bromobutane. The product C gives butane (C4H10) which is consistent. More precisely: cyclobutane -> heat -> but-1-ene [A]. But-1-ene + HBr -> 2-bromobutane [B] (Markovnikov). 2-bromobutane + Br2/CCl4 -> 2,3-dibromobutane... this doesn't easily give butane. Alternatively, [A] = 1-butene, [B] = 1-bromo-2-butene (allylic?). The listed option 'compound [B] is 1,4-dibromobutane' suggests [A] is 1,3-butadiene (from cyclobutane dehydrogenation), which adds HBr at positions 1,4 to give 1-bromo-2-butene or adds Br2 to give 1,4-dibromobutane. 1,4-dibromobutane on reduction (Zn/LiAlH4) gives butane. This matches! So: cyclobutane -> heat -> 1,3-butadiene [A] + H2. 1,3-butadiene + HBr -> 1-bromo-2-butene [B]. [B] + Br2/CCl4 -> 1,4-dibromo-2-butene [C] or 1-bromo-2,3-dibromobutane. Actually: [A] = CH2=CH-CH=CH2 (butadiene, from pyrolysis of cyclobutane). [B] = 1,2-dibromoethane? No, then molecular formula wrong. The option 'compound [B] is 1,4-dibromobutane' (original option C) suggests [A] does 1,4 addition of Br2 or forms 1,4-dibromobutane. Most consistent: [A] = 1,3-butadiene; [B] = 3-bromobutene-1 (HBr 1,4 addition); [C] = the Br2/CCl4 addition product. Given the final product C gives butane on reduction, and option C in the original says compound [B] is 1,4-dibromobutane, this appears to be the correct answer (compound B is 1,4-dibromobutane from Br2 + 1,3-butadiene in 1,4 addition).

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