Which one of the following is most Stable ?
3º carbocations are most stable.
To identify the most stable carbocation among the given options, we analyze their structures based on key stability factors:
From the images (though not visible here), we can infer the structures based on typical representations:
Carbocation stability follows the order:
Resonance stabilization (like allylic carbocations) provides additional stability beyond simple alkyl substitution.
Tertiary carbocations (3°) are more stable than secondary (2°), which are more stable than primary (1°). Allylic carbocations (resonance-stabilized) are exceptionally stable, often comparable to or greater than tertiary carbocations.
The most stable carbocation is the tertiary carbocation (Option 2), as it has maximum hyperconjugation and inductive stabilization. Allylic carbocations (Option 4) are also highly stable due to resonance, but tertiary generally outweighs secondary allylic unless resonance is extensive.
Stability order:
Hyperconjugation: Delocalization of σ-electrons from adjacent C-H bonds into the empty p-orbital of carbocation.
Resonance: Delocalization of π-electrons, as in allylic carbocations: