Question

The stability of carbanions in the following
(i) `RC-=overset(-)overset(..)C` , (ii)
(iii) `R_(2)C=overset(-)overset(..)CH` , (iv) `R_(3)C-overset(-)overset(..)CH_(2)`
is in the order
A. `(iv)gt(ii)gt(iii)gt(i)`
B. `(i)gt(iii)gt(ii)gt(iv)`
C. `(i)gt(ii)gt(iii)gt(iv)`
D. `(ii)gt(iii)gt(iv)gt(i).`

Answer 1

Correct Answer - C
The stability of carbanion decreases as the electronegativity of carbon carrying the -ve charge decreases or the hybridization of the carbon carrying the -ve charge changes from `sp-sp^(2)-sp^(3)`. Hence `RCequivC^(-)` (l) is the most stable while `R_(3)C-CH_(2)^(-)` (IV) is the least stable carbon anion. The carbon atom carrying the -ve charge in both `C_(6)H_(5)^(-)" and "RC = overset(-)CH` is `sp^(2)` hybridized. Out of these two `RC= CH^(-)` (iii) is less stable than `C_(6)H_(5)^(-)` (II) due to two R groups. `therefore` over all stability decreases in the order `(i)gt(ii)gt(iii)gt(iv)`