Question

The ease of dehydrohalogenation of $3^{\circ },2^{\circ }$ and $1^{\circ }$ alkyl halides with alcoholic $KOH$ is:

• A. $3^{\circ }>2^{\circ }>1^{\circ }$
• B. $3^{\circ }<2^{\circ }<1^{\circ }$
• C. $3^{\circ }>2^{\circ }<1^{\circ }$
• D. $3^{\circ }<2^{\circ }>1^{\circ }$

Answer 1

The correct option is A $3^{\circ }>2^{\circ }>1^{\circ }$

According to Saytzeff rule, any alkyl halide that gives a more highly substituted (more stable) alkene undergoes dehydrohahyenation faster than the one which gives a less highly substituted (less stable) alkane. Thus, the case of dehydrohalogenation of different alkyl halides having the same halogen decreases in the order: $3^{\circ }\left(\text{tertiary}\right)>2^{\circ }\left(\text{secondary}\right)>1^{\circ }\left(\text{Primary}\right)$