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Select the correct statement about electronic effects in organic chemistry.

1. Delocalisation of sigma-electrons is hyperconjugation.
2. Delocalisation of pi-electrons is resonance.
3. Permanent partial displacement of sigma-electrons is inductive effect.
4. Cyclopropylmethyl cation shows sigma-resonance.

Correct answer: Cyclopropylmethyl cation shows sigma-resonance.

Solution

Hyperconjugation involves sigma (C-H) electrons interacting with an adjacent pi or empty p orbital — not merely 'sigma electron delocalization' in general. Resonance involves pi electrons or lone pairs, not sigma electrons. Inductive effect is a permanent polarization through sigma bonds but is not a 'displacement' of those electrons themselves. The cyclopropylmethyl cation is correctly described as exhibiting sigma-resonance (Walsh orbital overlap with the carbocation).

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