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2,3-Dimethyl-2-butene can be prepared by heating which of the following compounds with a strong acid?
A
$(CH_3)_2C=CH-CH_2-CH_3$
B
$(CH_3)_2CH-CH_2-CH=CH_2$
C
$(CH_3)_2CH-CH(CH_3)-CH=CH_2$
D
$(CH_3)_3C-CH=CH_2$
Detailed Solution
$H^+$ adds to $(CH_3)_3C-CH=CH_2$ to give the secondary carbocation $(CH_3)_3C-\overset{+}{C}H-CH_3$.
A 1,2-methyl shift ($\sim CH_3$) gives the more stable tertiary carbocation $(CH_3)_2\overset{+}{C}-CH(CH_3)-CH_3$.
Loss of $H^+$ gives $(CH_3)_2C=C(CH_3)_2$, i.e. 2,3-dimethyl-2-butene.
A 1,2-methyl shift ($\sim CH_3$) gives the more stable tertiary carbocation $(CH_3)_2\overset{+}{C}-CH(CH_3)-CH_3$.
Loss of $H^+$ gives $(CH_3)_2C=C(CH_3)_2$, i.e. 2,3-dimethyl-2-butene.