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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0:55 minutes

Problem 23(c)

Textbook Question

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

Verified step by step guidance

Identify the conformation type (e.g., staggered, eclipsed, gauche, anti) based on the Newman projection or molecular diagram provided. This will help determine the relative positions of substituents around the bond of interest.

Locate the two substituents on adjacent carbons that are being used to define the dihedral angle (θ). These substituents are typically represented as groups attached to the front and back carbons in a Newman projection.

Define the dihedral angle (θ) as the angle between the planes formed by the bonds to these substituents. For example, in a staggered conformation, θ is typically 60°, 120°, or 180°, depending on the relative positions of the groups.

Use the molecular geometry or Newman projection to measure or deduce the dihedral angle. For example, if the substituents are directly opposite each other, θ = 180° (anti conformation). If they are adjacent, θ = 60° (gauche conformation).

Verify the calculated dihedral angle by considering the steric and electronic interactions between the substituents. This can help confirm whether the conformation is energetically favorable or unfavorable.

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Key Concepts

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

Dihedral Angle

The dihedral angle is the angle between two intersecting planes, specifically the angle formed by two sets of three atoms in a molecule. It is crucial in understanding the spatial arrangement of atoms and how they influence molecular conformation. In organic chemistry, dihedral angles help predict the stability and reactivity of different conformations of a molecule.

Conformational Analysis

Conformational analysis is the study of the different spatial arrangements of atoms in a molecule that can be interconverted by rotation around single bonds. This analysis is essential for understanding how molecular shape affects properties such as reactivity and interaction with other molecules. It involves identifying stable and unstable conformations based on steric and torsional strain.

Torsional Strain

Torsional strain arises from the repulsion between electrons in bonds that are eclipsed or close to each other during rotation around a bond. This strain affects the stability of different conformations, with staggered conformations generally being more stable than eclipsed ones. Understanding torsional strain is key to predicting the preferred conformations and their corresponding dihedral angles in organic molecules.

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Related Practice

Textbook Question

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

c. Begin your graph at the 0° dihedral angle and begin to turn the front carbon.

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.

Textbook Question

Draw a graph, similar to Figure 3-9, of the torsional strain of 2-methylpropane as it rotates about the bond between C1 and C2. Show the dihedral angle and draw a Newman projection for each staggered and eclipsed conformation.

Textbook Question

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

(a)

Textbook Question

For each of the pairs in Assessment 3.29, which conformation would you expect to be more prominent at equilibrium?

(a)

(b)

(c)

Textbook Question

Choose the conformation in each pair that is most stable. If both are equally stable, then write 'no difference.'

(a)

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)

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