Consider the reaction of 1,3-butadiene with HBr (in the dark, under an N ₂ atmosphere) at -15^ C . What is the correct order of the relative yields of the following alkenyl bromides? (I) (II) (III)

Step-by-step solution

The reaction of 1,3-butadiene with HBr in the dark and under an N ₂ atmosphere proceeds via an electrophilic addition mechanism. Protonation of 1,3-butadiene occurs at a terminal carbon to generate the most stable, resonance-stabilized allylic carbocation intermediate: CH₂=CH-CH=CH₂ + H^+ [ CH₃- + C H-CH=CH₂ CH₃-CH=CH- + C H₂ ] At low temperatures ( -15^ C ), the reaction is under kinetic control. The bromide ion ( Br^- ) attacks the carbocation at the secondary carbon (C2) faster than at the primary carbon (C4) be