Arrange the following carbanions in order of their decreasing stability.
(A) H3C – C ≡ C-
(B) H – C ≡ C-
(c) H3C – CH2-
Stability of carbanion depends on +I effect due to –CH3.
In (B) there is no –CH3 group attached thus there will be no +I effect and it will be the most stable carbanion out of the three. In (A) there is +I effect due to –CH3 group but the distance between –CH3 and negative charge is more that’s why it will be quite stable but less stable than (B). In (C) –CH3 s directly attached to the carbon containing negative charge so +I effect will be highest in this case and it will be the least stable one.
Order of their decreasing stability is (ii) B > A > C.