Which of the following will give same product with HBr in the presence or absence of peroxide?
A
Cyclohexene
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B
1-Methylcyclohexene
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C
1, 2-Dimethylcyclohexene
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D
1-Butene
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Solution
The correct option is C 1, 2-Dimethylcyclohexene The addition of HBr to an alkene in absence of peroxide obeys Markovnikov's rule.
Markovnikov's rule : Negative part of the addendum (adding molecule) gets attached to that doubly bonded C which posses lesser number of hydrogen atoms.
In the presence of peroxide, the addition of HBr to unsymmetrical alkenes gives Anti-markovnikov's rule i.e Br addition takes place at doubly bonded C which posses greater number of hydrogen atoms.
These two reactions differs when the alkene is unsymmetrical.
Symmetrical alkenes gives same product in presence and absence of peroxide.
Since compound (a) and (c) are symmetrical, they give same product on addition of HBr