See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Hyperconjugation and Delocalisation **Understanding Hyperconjugation:** Hyperconjugation involves the delocalisation of electron density from a $\sigma$ bond (typically $C-H$) into an adjacent $\pi$ system or empty orbital. **Key Mechanism:** - The electrons in a $C-H$ bond shift towards a nearby unsaturated system - This requires an electron-withdrawing site to accept electron density - The $C-H$ bond becomes partially polarised **Analysis of Options:** **(1) Unsaturated system:** ✓ Electrons delocalise INTO the $\pi$ system — this IS hyperconjugation **(2) Positively charged carbon ($C^+$):** ✓ An electrophilic carbon accepts electron density from adjacent $C-H$ bonds — this IS hyperconjugation **(3) Unpaired electron (radical):** ✓ The unpaired electron site can accept electron density from nearby $C-H$ bonds — this IS hyperconjugation **(4) Negatively charged carbon ($C^-$):** ✗ A negatively charged carbon is electron-rich and **repels** incoming electron density from $C-H$ bonds. This does NOT participate in hyperconjugation. **Answer: (4)** — Hyperconjugation involves delocalisation towards electron-deficient sites. A negatively charged carbon is electron-rich and cannot accept $C-H$ bond electrons, so it is the **exception**.