Let's solve the problem **step by step**: --- ## 1. **Understanding the Task** You are asked to graph the **energy profile of butane** as it rotates about the C2–C3 bond, plotting energy (kcal/mol) vs. dihedral angle (degrees). Then, you are to draw the lowest energy conformer in wedge-dash notation. --- ## 2. **Butane Conformational Analysis** - **Butane** (C₄H₁₀) has significant **conformational isomers** due to rotation about the C2–C3 bond. - The main conformers are: 1. **Anti** (180°): Lowest energy (methyl groups farthest apart) 2. **Gauche** (60°, 300°): Higher energy (methyl groups closer) 3. **Eclipsed** (°, 120°, 240°, 360°): Highest energy (methyl groups overlap with each other or with hydrogens) ### **Approximate Energies (kcal/mol)** - **Anti (180°)**: (reference, lowest) - **Gauche (60°, 300°)**: ~.9 - **Eclipsed (°, 360°)**: ~5. (methyls eclipse each other) - **Eclipsed (120°, 240°)**: ~3.6 (methyl eclipses a hydrogen) --- ## 3. **Plotting the Graph** ### **Label axes:** - **Y-axis:** Energy (kcal/mol) - **X-axis:** Dihedral angle about the C2–C3 bond (degrees) ### **Key points to plot:** | Dihedral Angle (°) | Conformation | Energy (kcal/mol) | |--------------------|------------------------|-------------------| | | Eclipsed (Me–Me) | 5. | | 60 | Gauche (Me–H) | .9 | | 120 | Eclipsed (Me–H) | 3.6 | | 180 | Anti (Me–Me staggered) | . | | 240 | Eclipsed (Me–H) | 3.6 | | 300 | Gauche (Me–H) | .9 | | 360 | Eclipsed (Me–Me) | 5. | **(Me = methyl, H = hydrogen)** ### **Shape of the curve:** - Peaks at ° (and 360°) and 180° are minima. - Local minima at 60° and 300° (gauche). - Local maxima at 120° and 240° (eclipsed with H). --- ## 4. **Drawing the Graph** You can sketch the plot using the table above. Here is a quick guide: - Plot each point as above. - Connect the dots smoothly to form a periodic curve. - Label the X-axis and Y-axis. - Title: "**Energy profile of butane by rotation about the C2–C3 bond**". --- ## 5. **Lowest Energy Conformer** - **Anti conformation** (180°): methyl groups are staggered and opposite each other. - **Wedge-dash drawing** for anti butane: ``` H H \ / C---C / \ CH3 CH3 ``` - Or with dashed and wedged bonds (for C2 and C3): ``` H \ C -- CH3 / \ H3C H ``` - Both methyl groups (CH₃) are **anti** to each other. --- ## 6. **Final Answer** ### **Step-by-step summary:** 1. **Plot the energy profile** as described above, using the values for each angle. 2. **Label the graph** as "Energy profile of butane by rotation about the C2–C3 bond". 3. **Draw the lowest energy conformer** using the wedge-dash notation for the anti conformation (180°). --- ### **Example Graph (ASCII Art)** ``` Energy (kcal/mol) | | /\/\ | / \ | / \ |_______/ \_______ 60 120 180 240 300 360 Dihedral angle (degrees) ``` --- ### **Wedge-dash lowest energy conformer (Anti):** ``` H \ C -- CH3 / \ H3C H ``` --- **You can now sketch the graph and the conformer as described above on your paper!** Let me know if you need a digital drawing or further clarification.