Question

The nucleophilicity order of halogens in polar aprotic solvent is

• A. $F^{-}>C{l}^{-}>B{r}^{-}>I^{-}$
• B. $F^{-}>I^{-}>B{r}^{-}>F^{-}$
• C. $F^{-}<C{l}^{-}<B{r}^{-}<I^{-}$
• D. $C{l}^{-}>F^{-}>B{r}^{-}>I^{-}$

Answer 1

The correct option is A $F^{-}>C{l}^{-}>B{r}^{-}>I^{-}$

In a group, nucleophilicity decreases as size of anion increases in polar aprotic solvent. It is because in such a solvent, the anion is not solvated and smaller the anion, higher the charge density and hence nucleophilic nature. Thus, the corrrect order of nucleophilicity is $F^{-}>C{l}^{-}>B{r}^{-}>I^{-}$. However this order is reversed in polar protic solvent.