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Question:

2,3-dimethyl-2-butene can be prepared by heating which of the following compounds with a strong acid?

(CH3)3C−CH=CH2

(CH3)2CH−CH2−CH=CH2

(CH3)2C=CH−CH2−CH3

(CH3)2CH−CH|CH3−CH=CH2

Solution:

(CH3)3C−CH=CH2Strongacid−−−−−−−−−−→ΔCH3C(CH3)=C(CH3)CH3In presence of strong acid, rearrangement reaction occurs.In the first step, a proton is added (CH3)3C−CH=CH2Strongacid−−−−−−−−−−→Δ(CH3)3C−CH+−CH3In the next step, a methyl group migrates (CH3)3C−CH+−CH3→(CH3)2C+−C(CH3)H−CH3In the last step, a proton is removed (CH3)2C+−C(CH3)H−CH3−H+−−−−→CH3C(CH3)=C(CH3)CH3