Which of the following is the correct order of decreasing $\mathrm{SN}^2$ reactivity?

Which of the following is the correct order of decreasing $\mathrm{SN}^2$ reactivity?
  1. $\mathrm{RCH}_2 \mathrm{X}>\mathrm{R}_3 \mathrm{CX}>\mathrm{R}_2 \mathrm{CHX}$
  2. $\mathrm{RCH}_2 \mathrm{X}>\mathrm{R}_2 \mathrm{CHX}>\mathrm{R}_3 \mathrm{CX}$
  3. $\mathrm{R}_3 \mathrm{CX}>\mathrm{R}_2 \mathrm{CHX}>\mathrm{RCH}_2 X$
  4. $\mathrm{R}_2 \mathrm{CHX}>\mathrm{R}_3 \mathrm{CX}>\mathrm{RCH}_2 \mathrm{X}$ $(\mathrm{X}=$ a halogen $)$

Solution

More is the steric hindrance at the carbon bearing the halogen, lesser is the $\mathrm{S}_{\mathrm{N}} 2$ reactivity. Hence, (B) is correct.

Asked in: JEE Main 2007

Practice more Halogen Derivatives questions on Aicharya