When neopentyl alcohol is heated with an acid, it slowly converted into an 85 : 15 mixture of alkenes A and B, respectively. What are these alkenes ?
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The Correct Option is B
Solution and Explanation
Step 2: A 1,2-methyl shift gives the much more stable tertiary carbocation \((\mathrm{CH_3})_2\mathrm{C^+{-}CH_2CH_3}\) (2-methylbut-2-yl cation).
Step 3: Loss of \(\mathrm{H^+}\) from the \(\mathrm{CH_2}\) group (towards the ethyl group) gives the more substituted alkene \((\mathrm{CH_3})_2\mathrm{C{=}CH{-}CH_3}\), 2-methylbut-2-ene (major, 85%, A, Saytzeff product).
Step 4: Loss of \(\mathrm{H^+}\) from a methyl group gives \(\mathrm{CH_2{=}C(CH_3){-}CH_2CH_3}\), 2-methylbut-1-ene (minor, 15%, B).
Step 5: This pair (2-methylbut-2-ene and 2-methylbut-1-ene) is shown in option (2). Options (1), (3) and (4) contain 3-methylbut-1-ene, which needs a hydride shift to a less stable secondary carbocation and is not formed.
Answer: (2) 2-methylbut-2-ene and 2-methylbut-1-ene
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