When 3-methyl-1-butene is reacted with concentrated , a carbocation intermediate forms which immedia — Reaction Mechanism Chemistry Question
Question
When 3-methyl-1-butene is reacted with concentrated $HCl$, a carbocation intermediate forms which immediately undergoes a rearrangement. In the final, most stable rearranged carbocation, what is the total number of $\alpha$ -hydrogens participating in hyperconjugation?
💡 Solution & Explanation
The addition of $H^+$ to 3-methyl-1-butene ($CH_2=CH-CH(CH_3)_2$) initially forms a secondary carbocation: $CH_3-C^+H-CH(CH_3)_2$. This intermediate undergoes a rapid 1,2-hydride shift to form the more stable tertiary carbocation: $CH_3-CH_2-C^+(CH_3)_2$. In this rearranged tertiary carbocation (the tert-amyl cation), the positively charged carbon is attached to two methyl groups (6 $\alpha$ -hydrogens) and one ethyl group (2 $\alpha$ -hydrogens). The total number of $\alpha$ -hydrogens is $6 + 2 = 8$.