Question

The correct order of leaving group ability in nucleophilic substitution reaction is

• A. $B{r}^{-}>C{l}^{-}>C{H}_{3}C{O}_2^{-}>H{O}^{-}>H^{-}$
• B. $H^{-}>H{O}^{-}>C{H}_{3}C{O}_2^{-}>C{I}^{-}>B{r}^{-}$
• C. $B{r}^{-}>C{H}_{3}C{O}_2^{-}>C{l}^{-}>H{O}^{-}>H^{-}$
• D. $C{H}_{3}C{O}_2^{-}>B{r}^{-}>C{l}^{-}>H{O}^{-}>H^{-}$

Answer 1

Answer: (A)

The leaving group ability decreases as the basicity of the nucleophile increases. Since the basicity increases in the order: $B{r}^{-}<C{l}^{-}<C{H}_{3}CO{O}^{-}<H{O}^{-}<H^{-}$, therefore, their leaving group ability decreases in the reverse order, i.e., $B{r}^{-}>C{l}^{-}>C{H}_{3}CO{O}^{-}>H{O}^{-}>H^{-}$. Thus, option (a) is correct.