Question

Arrange the following in the increasing order of their ability as a leaving group:
$C{H}_3{S}^{-},C{H}_3{O}^{-},C{F}_3^{-}$ and $F^{-}$

• A. $C{H}_3{S}^{-}$ > $C{H}_3{O}^{-}$ > $C{F}_3^{-}$ > $F^{-}$
• B. $C{H}_3{O}^{-}$ > $C{H}_3{S}^{-}$ > $F^{-}$ > $C{F}_3^{-}$
• C. $C{H}_3{S}^{-}$ > $C{H}_3{O}^{-}$ > $F^{-}$ > $C{F}_3^{-}$
• D. $C{H}_3{S}^{-}$ < $C{H}_3{O}^{-}$ < $C{F}_3^{-}$ < $F^{-}$

Answer 1

Answer: (C)

$C{H}_3{S}^{-}$ > $C{H}_3{O}^{-}$ > $F^{-}$ > $C{F}_3^{-}$

The decreasing order for the ability as leaving group is $C{H}_3{S}^{-}>C{H}_3{O}^{-}>F^{-}>C{F}_3^{-}$

Higher is the electronegativity of the atom bearing negative charge, more tightly are held the electron pairs and their donation is less likely. This decreases the electrophilic character. The decreasing order of electronegativity is $S>O>F$.

$C{F}_3^{-}$ is least nucleophilic in nature as three highly electronegative $F$ atoms significantly decrease the electron density on $C$ atom.