Question

Which of the following gives 2, 3-dimethyl but-2-ene?

• A. $\text{2,3-dimethylbutan-1-ol}\underset{\Delta }{\overset{H_{2}S{O}_4}{\to }}$
• B. $\text{2,3-dimethylbutan-2-ol}\underset{\Delta }{\overset{H_{2}S{O}_4}{\to }}$
• C. $\text{2,3-dimethyl -1-bromobutane}\stackrel{alcKOH}{\to }$
• D. $\text{2,3-dimethyl -2-bromobutane}\stackrel{alcKOH}{\to }$

Answer 1

Answer: (A), (B), (D)

$\text{2,3-dimethyl -2-bromobutane}\stackrel{alcKOH}{\to }$

2,3-dimethy-1- bromobutane gives 2,3-dimethyl but -1-ene as it is primary alkyl halide goes via $E2$ mechanism.
2,3-dimethyl -2-bromo butane is teritary alkyl halide. It gives more stable 2,3-dimethylbut-2-ene via $E2$ mechanism.
Both 2,3-dimethylbutan -1-ol and 2,3-dimethylbutan -2-ol gives stable saytzeff product, 2,3-dimethylbut-2-ene.