Question

Predict all the alkenes that would be formed by dehydrohalogenation of the following halide with sodium ethoxide in ethanol and identify the major alkene:

2-Chloro-2-methylbutane

Answer 1

2-Chloro-2-methylbutane has two different sets of equivalent β-hydrogens so that it will give 2 alkenes.

\[\begin{array}{cc}
\ce{\overset{β}{C}H3}\phantom{.................................}\ce{CH3}\phantom{..................}\ce{CH3}\phantom{..}\\
\phantom{}|\phantom{....................................}|\phantom{......................}|\phantom{....}\\
\ce{\overset{β}{C}H3 - C - \overset{β}{C}H2CH3 ->[C2H5ONa/C2H5OH][-HCl] \underset{2-Methylbut-1-ene}{CH2 = C - CH2CH3} + \underset{2-Methylbut-2-ene}{CH3 - C = CHCH3}}\\
|\phantom{...............................................................}\\
\ce{\underset{2-Chloro-2-methylbutane}{Cl}}\phantom{..............................................................}
\end{array}\]

Since the more substituted alkene will be more stable, 2-methylbut-2-ene will be the major alkene.