See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Identifying Non-Nucleophiles **Definition of a nucleophile:** A species with lone pairs or π-electrons that can donate electron density to an electrophilic center. **Analysis of each option:** **(1) $Br^-$** — Nucleophile ✓ - Negative charge with lone pairs; readily donates electrons to electrophiles **(2) $\ddot{NH_3}$** — Nucleophile ✓ - Lone pair on nitrogen; acts as a Lewis base and nucleophile in $S_N2$ reactions **(3) $SO_3$** — **Not a nucleophile** ✗ - $SO_3$ is **electrophilic**, not nucleophilic - Sulfur is electron-deficient (only 6 electrons around S, no lone pairs) - Acts as an electrophile in electrophilic aromatic substitution reactions - Accepts electron density rather than donates it **(4) $C_6H_6$ (benzene)** — Nucleophile ✓ - π-electrons of the aromatic ring act as nucleophiles - Participates in electrophilic aromatic substitution ($S_E^{Ar}$) **Answer: (3) $SO_3$** is not a nucleophile because it is an electrophile—it lacks lone pairs and seeks electron density from π-systems rather than providing it.