Question

Give reason for the following

CH₂ = CH^- is more basic than HC ≡ C^-.

Answer 1

CH₂ = CH^- is more basic than HC≡C^- because electronegativity of C^- of HC≡ C^- is higher in comparison to such carbon of CH₂ = CH^- .

In H-C≡C^-, C-atom is sp-hybridised while in CH₂=CH^-C-atom is sp²-hybridised. So, in C-atom of CH ≡ C^-, s-orbital character (50%) is higher than that of CH₂ =CH^-(33 .3%) . On the basis of attraction of electron in orbital  s> p> d > f, the electron attraction tendency of such C-atom of CH≡ C^-is higher than that of CH₂ = CH^-

So, rate of donation of a pair of electron in CH₂ = CH^- it higher than that of HC≡C^- because basic strength is directly proportional to rate of donation of free pair of electron.

Hence, due to above reason CH₂ = CH^- is more basic than CH≡ C^-.