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Q.
Propene is more reactive than ethene towards $HBr$ because
Hydrocarbons
Solution:
Addition of HBr to ethene takes place by electrophilic addition mechanism
$\underset{\text{ethene}}{CH _{2}= CH _{2}} \xrightarrow{HBr} \underset{\text{Ethyl bromide}}{CH _{2} CH _{2} Br}$
Mechanism $\Rightarrow CH _{2}= CH _{2} \xrightarrow{H ^{+} Br ^{-}} \underset{(i)}{ CH _{3}} \overset{\oplus}{ CH _{2}} \xrightarrow{ Br ^{-}}CH _{3} CH _{2} Br$
Addition of HBr to propene takes place by electrophilic addition mechanism in accordance with Markonikov rule, according to which the negative part of the adding molecule gets attached to that carbon atom
$CH _{3}- CH = CH _{2} \xrightarrow{ HBr} CH _{3}-\underset{\overset{|}{Br}}{CH}- CH _{3}$
