Question

Which of the following has the highest reactivity towards an electrophilic addition reaction?

• A. Ethane
• B. 2-methyl-2-butene
• C. Propene
• D. 2-butene

Hint:

Compare how many alkyl groups are attached to each double bond; more substitution means more reactivity here.

Answer 1

The Correct Option is B

Step 1: Electrophilic addition reactions occur at the carbon-carbon double bond of alkenes; electron rich double bonds react faster because they attack the electrophile more readily and because the resulting carbocation intermediate is better stabilized.

Step 2: Alkyl groups attached to a double bond donate electron density into it through hyperconjugation and the inductive effect, and they also stabilize the carbocation formed during addition. So the more alkyl substituted a double bond is, the more reactive it is toward electrophilic addition.

Step 3: Rank the given options by degree of substitution at the double bond. Ethane has no double bond at all; it is a saturated alkane and essentially does not undergo electrophilic addition. Propene, \( CH_2=CH-CH_3 \), is monosubstituted. 2-butene, \( CH_3-CH=CH-CH_3 \), is disubstituted. 2-methyl-2-butene, \( (CH_3)_2C=CH-CH_3 \), is trisubstituted, carrying three alkyl groups on its double bond carbons.

Step 4: Since 2-methyl-2-butene has the greatest number of electron donating alkyl groups on its double bond, it has the most electron rich double bond and forms the most stable carbocation intermediate, making it the most reactive toward electrophilic addition.

\[ \boxed{\text{2-methyl-2-butene}} \]