Q5P The 1,2 adduct and the 1,4 adduc... [FREE SOLUTION]

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Chapter 14: Q5P (page 430)

The 1,2 adduct and the 1,4 adduct formed by reaction of HBr with 1,3-butadiene are in equilibrium at 40 掳C. Propose a mechanism by which the interconversion of products takes place.

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Hydrohalogenation of alkene

Hydrohalogenation of alkene or addition of hydrogen halide H-X, e.g., HCl, HBr, HI on alkene to form the haloalkane.

This reaction is carried out in two ways:

Direct passing of H-X on alkene
By using a polar solvent

This reaction formed the carbocation intermediate, and its stability only decides the product alkyl halide

Interconversion of 3-Bromo-1-butene and 1-Bromo-2-butene

Allylic halide 3-Bromo-1-butene and 1-Bromo-2-butene will undergo slow dissociation to form the stabilized allylic carbocation through $S_{N} 1$ reaction.

Both the allylic halides form the same allylic carbocation on dissociation. The addition of bromide ion (act as a nucleophile) on allylic carbocation formed the mixture of Bromobutene: 3-Bromo-1-butene and 1-Bromo-2-butene.

The reaction is running under equilibrium conditions the stable thermodynamic 1-Bromo-2-butene predominates.