Q7-66E - Organic Chemistry (Mcmurry)

Question

Vinylcyclopropane reacts with HBr to yield a rearranged alkyl bromide. Follow the flow of electrons as represented by the curved arrows, show the structure of the carbocation intermediate in brackets, and show the structure of the final product.

 

Step-by-Step Solution

Answer

The structure of the carbocation intermediate and final product is,

Step 1: Alkenes with HBr

The reaction of an alkene with HBr forms alkyl halides. The first step is the generation of carbocation intermediate when alkene undergoes protonation of the pi bond. The second step is the reaction with the bromide ion.

Step 2: The structure of the carbocation intermediate and the final product

When vinylcyclopropane is treated with HBr, there is an attack of $\mathrm{\pi }$ double bond electrons present in vinylcyclopropane on H⁺ takes place. A carbocation is formed, which is pictured in the far right position of the diagram below. An alkyl shift forms the intermediate shown in the bracket, which further reacts with bromide ion to yield 1-bromo-2-methylcyclobutane.

 

                                          Reaction of vinylcyclopropane with HBr