Question

In: Chemistry

Reaction of HBr with 3-methylcyclohexene yields a mixture of four products

 

Reaction of HBr with 3-methylcyclohexene yields a mixture of four products: cis-and trans-1-bromo-3-methylcyclohexane and cis-and trans-1-bromo-2-methylcyclohexane. The analogous reaction of HBr with 3-bromocyclohexene yields trans-1, 2-dibromocyclohexane as the soleproduct.

Draw structures of the possible intermediates, and then explain why only a single product is formed in this reaction.

Solutions

Expert Solution

Given chemical reactions,

 

Reaction of HBr with 3-methylcyclohexene,

The attack of the electrons of the double bond in 3-methyl cyclohexene on the positively polarized hydrogen of HBr yields two carbocations of almost equal stabilities. These carbocations being planar can be attacked by the bromide ion from top to bottom faces to yield four different products. 

Reaction of HBr with 3-bromocyclohexene,

The attack of the electrons of the double bond in 3-bromocyclohexene on the positively polarized hydrogen of HBr yields two carbocations but one carbocation is unstable. This led to the formation of cyclic bromonium ions.  then bromide ion attacked from opposite side leads to the formation of trans 1,2 di-bromocyclohexane. 

 


Answers can be found in the Explanation section.

 

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