Question

3-Methyl-pent-2-ene on reaction with HBr in presence of peroxide forms an addition product. The number of possible stereoisomers for the product is ______.

Options

• Six

• Zero

• Two

• Four

Answer 1

3-Methyl-pent-2-ene on reaction with HBr in presence of peroxide forms an addition product. The number of possible stereoisomers for the product is four.

Explanation:

Addition of HBr on 3-metbylpent-2-ene in presence of peroxide, takes place according to anti-Markovnikov's rule.

\[\begin{array}{cc}
\phantom{..}\ce{CH3}\phantom{.......................}\ce{Br}\phantom{....}\ce{CH3}\phantom{..}\\
\phantom{.}|\phantom{..........................}|\phantom{......}|\phantom{...}\\
\phantom{}\ce{\overset{1}{C}H3 - \underset{3-Methylpent-2-ene}{\overset{2}{C}H = \overset{3}{C} - \overset{4}{C}H2}\overset{5}{C}H3 ->[HBr][-H2O]\underset{\underset{(2 chiral centres)}{2-Bromo-3-methylpentane}}{CH3 - \underset{\bullet}{C}H - \underset{\bullet}{C}H - CH2 - CH3}}
\end{array}\]

Since two chiral centres are present in the product, four stereoisomers (2ⁿ) are possible.