The stability of carbanions in the following:
(i) `RC-=C^(Theta)` (ii) (iii) `R_(2)C=overset(Theta)CH` (iv) `R_(3)C-overset(Theta)CH_(2)` in the order of: (iv) `gt` (ii) `gt` (iii) `gt` (i); (i) `gt` (iii) `gt` (ii) `gt` (iv); (i) `gt` (ii) `gt` (iii) `gt` (iv); (ii) `gt` (iii) `gt` (iv) `gt` (i)

Options

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

C

Explanation

The stability of the carbanion decreases as the electronegativity of the carbon carrying the -ve charge decreases or the hybridization of the carbon carrying the -ve charge changes from `sp-sp^(2)-sp^(3)`. Thus, `RC-=C^(-)` (i) is the most stable while `R_(3)C-CH_(2)^(-)` (iv) is the least stable carbanion. The carbon atom carrying the -ve charge in both `C_(6)H_(5)^(-)` and `R_(2)C=CH^(-)` is `sp^(2)`-hybridized. Out of these two, `R_(2)C=CH^(-)` (iii) is less stable than `C_(6)H_(5)^(-)` (ii) due to +I-effect of the two R groups. Thus, the overall stability decreases in the order: (i) `gt` (ii) `gt` (iii) `gt` (iv), ie,