See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Identifying the Strongest Base **Step 1: Recognize the basicity sources** - (a) Primary amine ($-NH_2$) on aliphatic carbon; imine ($C=NH$) present - (b) Primary amine ($-NH_2$) on guanidinium group attached to benzene - (c) Guanidinium group ($H_2N-C(=NH)-NH_2$) as free base - (d) Guanidinium group with methyl substitution on carbon **Step 2: Compare amine vs. guanidinium basicity** Primary amines are weak bases. Guanidinium groups are **much stronger bases** because the positive charge on the conjugate acid is delocalized over three nitrogen atoms through resonance, making it highly stable. **Step 3: Evaluate each guanidinium compound** - (b): Guanidinium attached to benzene ring (electron-withdrawing via inductive effect) - (c): Free guanidinium base with no substituents - (d): Guanidinium with methyl group (minor electron-donating effect) **Step 4: Effect of electron-withdrawing groups** The benzene ring in (b) is **electron-withdrawing**, which stabilizes the conjugate acid excessively and makes the free base less basic. In (c), there are no electron-withdrawing groups, so the nitrogen atoms are more electron-rich and available for protonation. **Step 5: Conclusion** Compound (c) has the highest basic strength because the unsubstituted guanidinium group has maximum electron density on nitrogen atoms without competing electron-withdrawing effects. **Answer: (c)**