Question

Which of the following reactivity orders is/are correct?

• A. $CH _{3}- CH = CH _{2}> CH _{2}= CH _{2}$ (towards electrophilic addition reaction)
• B. $CH _{2}= CH _{2}> CH _{2}- CH = CH _{2} \quad$ (towards catalytic hydrogenation)
• C. $CH _{2}= CH _{2}> H - C \equiv C - H$ (towards electrophilic addition)
• D. All of these are correct

Answer 1

Answer: (D)

Electrophillic addition reaction involves formation of a carbocation.

More stable carbocation is formed in propene than ethene.

Catalytic hydrogenation is not an electrophillic addition reaction. Rather, stability of alkene is to be kept in mind.

Since, propene is more stable than ethene (on the basis of hyper conjugation), it is less reactive towards hydrogenation.

Carbocation in electrophilic addition on ethene involves $1^{\circ}$ carbocation which is relatively more stable than vinyl carbocation in case of ethyne. So, ethene is more reactive than ethyne towards electrophilic addition.