CH2 = CH – CH3 CH2 = CH – CH2–Br
Select correct reagent for this reaction
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This reaction converts propene (CH2=CH–CH3) to allyl bromide (CH2=CH–CH2–Br), which is an allylic bromination. This requires a reagent that selectively brominates the allylic carbon (the CH2 group next to the double bond), not the double bond itself.
N-Bromosuccinimide (NBS) is the specific reagent for free-radical allylic bromination. It provides a low, constant concentration of Br2, which generates the bromine radical (Br•) needed to abstract an allylic hydrogen, leading to the desired product.
The other reagents are incorrect: Br2/H2O and HOBr perform bromohydrin formation (adding OH and Br across the double bond). Br2/CCl4 performs electrophilic addition, adding Br and Br across the double bond.
Final Answer: NBS