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

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1:02 minutes

Problem 54e

Textbook Question

For each pair of conformations shown, choose which is most stable. [If both conformations have the same number of gauche interactions, choose the one where the interactions are between smaller groups.]
(e)

Verified step by step guidance

Step 1: Understand the concept of conformational stability. Stability in conformations is influenced by steric hindrance and gauche interactions. Gauche interactions occur when two substituents are separated by a dihedral angle of approximately 60°, leading to increased steric strain.

Step 2: Analyze the conformations provided in the problem. Identify the substituents attached to the molecule and their relative positions in each conformation. Look for any gauche interactions between substituents.

Step 3: Count the number of gauche interactions in each conformation. If one conformation has fewer gauche interactions, it is more stable. Use the formula for dihedral angles to identify gauche interactions:

60°

Step 4: If both conformations have the same number of gauche interactions, compare the size of the groups involved in the interactions. Smaller groups cause less steric strain, making the conformation with smaller interacting groups more stable.

Step 5: Choose the most stable conformation based on the analysis above. Ensure that you consider both the number of gauche interactions and the size of the groups involved in those interactions.

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Key Concepts

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

Conformational Analysis

Conformational analysis involves studying the different spatial arrangements of a molecule that can be interconverted by rotation around single bonds. These conformations can significantly influence the stability and reactivity of the molecule. Understanding the energy associated with each conformation helps predict which arrangement is more stable under given conditions.

Gauche Interactions

Gauche interactions occur when two substituents on adjacent carbon atoms are positioned 60 degrees apart in a staggered conformation. These interactions can introduce steric strain, making certain conformations less stable. In evaluating stability, conformations with fewer or less significant gauche interactions are generally preferred, especially when comparing larger groups.

Steric Hindrance

Steric hindrance refers to the repulsion between atoms that occurs when they are brought close together, often due to their size. In conformational analysis, larger substituents can create more steric hindrance, leading to increased energy and decreased stability of a conformation. Thus, when comparing conformations, those with smaller groups experiencing less steric hindrance are typically more stable.

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Textbook Question

In Chapter 5, we introduce reaction coordinate diagrams as a plot of potential energy versus the progress of a reaction. Consider the reaction coordinate diagram drawn for the 'reaction' of conformation A becoming conformation B. Which structure is present at the top of the hill?

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Textbook Question

Which conformation in each of the following pairs has the least strain energy?

(c)

Textbook Question

Construct a graph, similar to Figure 3-11, of the torsional energy of 3-methylpentane along the C2―C3 bond.

e. Indicate which conformations are the most stable (lowest energy) and the least stable (highest energy).

Textbook Question

Why is it incorrect to say that the dihedral angle shown is 120° or even 109°?

Textbook Question

For each pair of conformations shown, choose which is most stable. [If both conformations have the same number of gauche interactions, choose the one where the interactions are between smaller groups.]

(f)

Textbook Question

Which of the following structures represent the same compound? Which ones represent different compounds?

(f)

Textbook Question

Construct a graph, similar to Figure 3-11, of the torsional energy of 3-methylpentane along the C2―C3 bond.

a. Place C2 in front, represented by three bonds coming together in a Y shape, and C3 in back, represented by a circle with three bonds pointing out from it.

b. Define the dihedral angle as the angle between the methyl group on the front carbon and the ethyl group on the back carbon.

Textbook Question

Calculate the dihedral angle (θ) for the conformations shown.

(c)

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