Question

Arrange the following alkyl halides in increasing order of the rate of $\beta$-elimination reaction with alcoholic $KOH$.

• A. $\left(ii\right)>\left(iii\right)>\left(i\right)$
• B. $\left(iii\right)>\left(ii\right)>\left(i\right)$
• C. $\left(i\right)>\left(ii\right)>\left(iii\right)$
• D. $\left(ii\right)>\left(i\right)>\left(iii\right)$

Answer 1

The correct option is B $\left(iii\right)>\left(ii\right)>\left(i\right)$

Rate of dehydrohalogenation in alkyl halide is depends on the stability of the alkene product formed.
More substituted alkenes are more stable.
Tertiary alkyl halides gives more substituted alkene compared to secondary which gives more substituted alkene than primary.
Hence, the rate of dehydrohalogenation in alkyl halide follows order, $\Rightarrow 3^{\circ }>2^{\circ }>1^{\circ }$.
Hence, correct order is $\left(iii\right)>\left(ii\right)>\left(i\right)$