Question

Explain why (CH₃)₃ C⁺ is more stable than so CH₃ CH⁺₂ and CH⁺₃ is the least stable cation?

Answer 1

(CH₃)₃C⁺ has nine a-hydrogens and hence has nine hyperconjugation structures while CH₃CH₂⁺ has only three a-hydrogens and has hence has only three hyperconjugation structures. As a result, (CH₃)₃C⁺ is more stable than CH₃CH₂⁺.  In contrast in CH, the vacant p-orbital is perpendicular filt to the plane in which C-H bond lie and hence cannot overlap with it. Thus, CH₃⁺ is not stabilized by hyperconjugation and is the least stable of the three cations.