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  4. The ascending order of stability of the carbanion H3 overset-C(P), C6H5 overset-CH2(Q), (CH3)2 overset-CH(R) and H2 overset-C -C H = C H2(S) is

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Q. The ascending order of stability of the carbanion
$H_3\overset{-}{C}(P)$, $C_6H_5\overset{-}{C}H_2(Q)$, $(CH_3)_2\overset{-}{C}H(R)$ and $H_2\overset{-}{C} -C H = C H_2(S)$ is

UP CPMTUP CPMT 2015Organic Chemistry – Some Basic Principles and Techniques

Solution:

Stability of carbanions is enhanced by
(i) presence of conjugation
(ii) presence of group exerting -$I$ effect. So, the correct order is
$\underset{\text{(Q)}}{{C_{6}H_{5} \overset{-} {C}H_{2}}} >\, H_{2} \overset{-} {C} — \underset{\text{(S)}}{{CH}} = CH_{2} >\, \underset{\text{(P)}}{{\overset{-} {C}H_{3}}}>\, \underset{\text{(R)}}{{(CH_{3})_{2}\overset{-} {C}H}}$