Heated with concentrated $H X_{3} PO X_{4}$ , the major alkene from which of these alcohols is formed from a carbocation that has undergone a 1,2-shift?

A3-methylbutan-2-ol
B2-methylbutan-2-ol
C3,3-dimethylbutan-2-ol
D3-methylpentan-3-ol

Answer: A, C

3-Methylbutan-2-ol: secondary cation, hydride shift to tertiary. 3,3-Dimethylbutan-2-ol: secondary cation, methyl shift to tertiary. 2-Methylbutan-2-ol and 3-methylpentan-3-ol already give tertiary cations, so the major alkene forms directly with no shift.

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Heated with concentrated HX3​POX4​, the major alkene from which of these alcohols is formed from a carbocation that has undergone a 1,2-shift?

Answer: A, C

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Heated with concentrated $H X_{3} PO X_{4}$ , the major alkene from which of these alcohols is formed from a carbocation that has undergone a 1,2-shift?