Reactivity of alkenes towards HX decreases in the order

see full answer

Your Exam Success, Personally Taken Care Of

1:1 expert mentors customize learning to your strength and weaknesses – so you score higher in school , IIT JEE and NEET entrance exams.

An Intiative by Sri Chaitanya

Ethene > Propene > Butene

Butene > Ethene > Propene

Butene > Propene > Ethene

None of these

answer is A.

(Unlock A.I Detailed Solution for FREE)

Best Courses for You

JEE

NEET

Foundation JEE

Foundation NEET

CBSE

Detailed Solution

Reactivity of Alkenes towards HX

Key Principle

The reaction intermediate of electrophilic addition is carbocation. Therefore, reactivity of alkene will depend on the stability of carbocation formed during the reaction.

Carbocation Stability Order

Tertiary > Secondary > Primary

The more stable the carbocation, the faster the electrophilic addition proceeds.

Alkene Structures and Their Carbocations

Alkene	Structure	Carbocation Formed	Type
(CH₃)₂C=CH₂	2-methylpropene	(CH₃)₃C⁺	Tertiary
CH₃CH=CH₂	Propene	CH₃CH⁺CH₃	Secondary
CH₂=CH₂	Ethene	CH₃CH₂⁺	Primary

Reactivity Order towards HX (Decreasing Order)

(CH₃)₂C=CH₂ > CH₃CH=CH₂ > CH₂=CH₂

Explanation: 2-methylpropene forms the most stable tertiary carbocation, making it the most reactive towards HX. Ethene forms the least stable primary carbocation, making it the least reactive.