Question

The correct order of stability of the following carbanions is:

$(C{H}_3{)}_3{C}^{-}{,}^{-}CC{l}_3,(C{H}_3{)}_{2}C{H}^{-},C_6{H}_5-C{H}_2^{-}$

• A. ${}^{-}CC{l}_3>C_6{H}_5-C{H}_2^{-}>(C{H}_3{)}_{2}C{H}^{-}>(C{H}_3{)}_3{C}^{-}$
• B. $C_6{H}_5-C{H}_2^{-}{>}^{-}CC{l}_3>(C{H}_3{)}_{2}C{H}^{-}>(C{H}_3{)}_3{C}^{-}$
• C. $C_6{H}_5-C{H}_2^{-}{>}^{-}CC{l}_3>(C{H}_3{)}_3{C}^{-}>(C{H}_3{)}_{2}C{H}^{-}$
• D. None of the above

Answer 1

The correct option is A

${}^{-}CC{l}_3>C_6{H}_5-C{H}_2^{-}>(C{H}_3{)}_{2}C{H}^{-}>(C{H}_3{)}_3{C}^{-}$

The trichloromethyl carbanion is the most stable because of the stabilizing effect of

three highly electronegative chlorine atoms. Methyl groups are electron-donating via

+I effect. The benzyl carbanion has some stabilization in the form of resonance.

Hence the correct order is:

${}^{-}CC{l}_3>C_6{H}_5-C{H}_2^{-}>(C{H}_3{)}_{2}C{H}^{-}>(C{H}_3{)}_3{C}^{-}$