Question

Alkenes are more reactive than alkynes toward addition of electrophilic reagents (e.g. $Br_{2}$, HBr, etc.) yet it is easy to stop the reaction at the alkene stage when 1 molar equivalent of the reagent is used. Explain.

Answer 1

On adding electrophilic reagents like ${Br}_{2}$, HBr Alkanes are more reactive than Alkynes.

This is because, In alkynes the pie-electrons are  tightly held by the  atoms of carbon due to the triple bond. And in alkenes the pie electrons are not held tight because of ${ sp }^{ 2 }$ hybridilized carbon atoms. The electrons become more delocalized and stable, so the pie electrons are less available for adding electrophilic reagents.  

Therefore, Alkynes reacts less than the Alkenes with electrophiles.