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Question:

Arrange the carbanions, (CH3)3C⁻, CCl3⁻, (CH3)2CH⁻, C6H5CH2⁻, in order of their decreasing stability.

CCl3⁻ > C6H5CH2⁻ > (CH3)2CH⁻ > (CH3)3C⁻

C6H5CH2⁻ > CCl3⁻ > (CH3)3C⁻ > (CH3)2CH⁻

(CH3)2CH⁻ > CCl3⁻ > C6H5CH2⁻ > (CH3)3C⁻

(CH3)3C⁻ > (CH3)2CH⁻ > C6H5CH2⁻ > CCl3⁻

Solution:

Due to the -I effect of three chlorine atoms and due to p-d π bonding, CCl₃⁻ is extra stable. Carbanion follow stability order. CCl3⁻ > C6H5CH2⁻ > (CH3)2CH⁻ > (CH3)3C⁻. In C6H5CH⁻, the -M effect delocalizes the -ve charge on carbon. The CH3 group in 1st and 3rd destabilizes the -ve charge on carbon.