Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

4. Alkanes and Cycloalkanes

Newman Projections

Organic Chemistry

4. Alkanes and Cycloalkanes

Newman Projections

Previous problemNext problem

8:58 minutes

Problem 13

Textbook Question

Draw a graph, similar to Figure 3-11, of the torsional energy of 2-methylbutane as it rotates about the C2—C3 bond.

Verified step by step guidance

Step 1: Understand the concept of torsional energy. Torsional energy arises due to the rotation around a bond, leading to different conformations with varying energy levels. In this case, the rotation is around the C2—C3 bond in 2-methylbutane.

Step 2: Analyze the provided graph (Figure 3-11). The graph shows the torsional energy changes as the molecule rotates around a bond, with specific conformations labeled (e.g., totally eclipsed, gauche, anti, etc.). The energy peaks correspond to eclipsed conformations, while valleys correspond to staggered conformations.

Step 3: Identify the key conformations for 2-methylbutane. Similar to the graph for butane, the conformations include totally eclipsed (highest energy), gauche (intermediate energy), anti (lowest energy), and eclipsed (higher energy but less than totally eclipsed). The substituents on the C2 and C3 carbons (CH3 and H groups) will influence the energy levels.

Step 4: Sketch the graph. Start by plotting the x-axis as the dihedral angle (θ) from 0° to 360° and the y-axis as the potential energy. Mark the energy peaks at 0° and 360° for the totally eclipsed conformation, intermediate peaks at 120° and 240° for eclipsed conformations, and valleys at 60° and 300° for gauche conformations, with the lowest valley at 180° for the anti conformation.

Step 5: Label the graph. Indicate the conformations (totally eclipsed, gauche, anti, eclipsed) at their respective angles and energy levels. Ensure the energy values are consistent with the substituent interactions in 2-methylbutane, similar to the pattern shown in Figure 3-11.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Torsional Strain

Torsional strain arises from the repulsion between electron clouds in eclipsed conformations of a molecule. In the case of 2-methylbutane, as it rotates around the C2—C3 bond, the energy changes due to the varying degrees of overlap between the hydrogen atoms. This strain is a key factor in determining the stability of different conformations.

Conformational Analysis

Conformational analysis involves studying the different spatial arrangements of a molecule that can be interconverted by rotation around single bonds. For 2-methylbutane, this analysis helps identify the most stable conformations (like anti and gauche) and the energy barriers between them, which are illustrated in the torsional energy graph.

Potential Energy Diagram

A potential energy diagram visually represents the energy changes of a molecule as it undergoes conformational changes. In the case of 2-methylbutane, the graph shows energy minima and maxima corresponding to different conformations, allowing for a clear understanding of the stability and energy costs associated with each conformation during rotation about the C2—C3 bond.

Watch next

Master How sigma bond rotation is visualized with a bite sized video explanation from Johnny

Start learning