Let's go through each part step by step for guanine: --- ## **a) Identify the hybridization of each nitrogen atom indicated.** We will label the indicated nitrogen atoms as \( N_1, N_2, N_3, N_4 \) (clockwise from the top left, as shown by the arrows). ### **Step-by-step hybridization:** #### **1. $N_1$ (Top, double-bonded to C, attached to H)** - Attached to 2 atoms (C, H), 1 lone pair, and involved in aromatic ring. - **Hybridization:** $sp^2$ #### **2. $N_2$ (Right, in amine group, attached to 2 H)** - Attached to 1 C, 2 H, 1 lone pair. - **Hybridization:** $sp^3$ #### **3. $N_3$ (Bottom, in ring, double-bonded to C)** - Attached to 2 atoms (C, C), 1 lone pair, involved in aromatic ring. - **Hybridization:** $sp^2$ #### **4. $N_4$ (Left, single-bonded in ring)** - Attached to 2 atoms (C, C), 1 lone pair, involved in aromatic ring. - **Hybridization:** $sp^2$ --- ## **b) For each nitrogen atom, identify the orbital the lone pair is occupying.** ### **Step-by-step:** #### **1. $N_1$ ($sp^2$)** - Lone pair is in an **sp² orbital** (perpendicular to the p orbital involved in the aromatic π system). #### **2. $N_2$ ($sp^3$)** - Lone pair is in an **sp³ orbital** (not involved in aromaticity). #### **3. $N_3$ ($sp^2$)** - Lone pair is in an **sp² orbital** (same as above). #### **4. $N_4$ ($sp^2$)** - Lone pair is in a **p orbital**, contributing to the aromatic π system. --- ## **c) Is the molecule aromatic, non-aromatic, or anti-aromatic?** ### **Step-by-step:** #### **Aromaticity criteria:** 1. **Planarity**: The molecule must be planar. 2. **Cyclic**: The molecule must be cyclic. 3. **Conjugation**: There must be a continuous ring of p orbitals (conjugation). 4. **Hückel's Rule**: Must have \(4n+2\) π electrons. #### **Count π electrons in ring:** - **C=C double bonds:** 2 (each contributes 2 π electrons) = 4 electrons - **N_4** (left): lone pair in p orbital = 2 electrons Total π electrons in the ring: **6 π electrons** #### **Apply Hückel's Rule:** - \(4n+2 = 6 \implies n=1\) - Satisfies Hückel's rule #### **Conclusion:** - The molecule is **aromatic**. --- ## **Final Answers** ### **a) Hybridization:** - $N_1$: $sp^2$ - $N_2$: $sp^3$ - $N_3$: $sp^2$ - $N_4$: $sp^2$ ### **b) Lone Pair Orbital:** - $N_1$: $sp^2$ - $N_2$: $sp^3$ - $N_3$: $sp^2$ - $N_4$: p orbital (participates in aromaticity) ### **c) Aromaticity:** - **Guanine is aromatic** (planar, cyclic, conjugated, 6 π electrons; satisfies Hückel’s rule). --- **Let me know if you'd like a diagram or further clarification!**