Electronic effects: inductive, resonance, hyperconjugation

Why this is asked: Hyperconjugation needs a C–H (or C–C) sigma bond directly attached to an sp² carbon — more such adjacent H's means more stability, which is why carbocation and alkene stability both rise with the number of alkyl-substituted carbons. Inductive effect fades with distance through sigma bonds; resonance doesn't fade the same way, but does need the participating orbitals to be coplanar — twist them out of plane and resonance stops working even though the atoms are still technically conjugated.

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