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

Drawing Newman Projections

Organic Chemistry

4. Alkanes and Cycloalkanes

Drawing Newman Projections

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2:26 minutes

Problem 40a

Textbook Question

Draw all the staggered and eclipsed conformers that result from rotation about the C-2-C-3 bond of pentane.

Verified step by step guidance

Identify the structure of pentane and locate the C-2 and C-3 bond. Pentane is a straight-chain alkane with the molecular formula C5H12. The C-2 and C-3 bond is the second carbon-carbon single bond in the chain.

Understand the concept of conformers. Conformers are different spatial arrangements of a molecule that result from rotation about a single bond. For the C-2-C-3 bond, rotation will lead to staggered and eclipsed conformations.

Draw the Newman projection for the C-2-C-3 bond. In a Newman projection, the front carbon (C-2) is represented as a dot, and the back carbon (C-3) is represented as a circle. The substituents on each carbon are drawn as lines radiating from the dot and circle.

Systematically rotate the back carbon (C-3) relative to the front carbon (C-2) in 60° increments. For each 60° rotation, draw the resulting conformer. This will include three staggered conformers (where the substituents on the front and back carbons are as far apart as possible) and three eclipsed conformers (where the substituents on the front and back carbons overlap).

Label each conformer as either staggered or eclipsed, and note the relative energy of each conformer. Staggered conformers are generally lower in energy due to reduced torsional strain, while eclipsed conformers are higher in energy due to increased torsional strain.

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Key Concepts

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

Conformational Isomerism

Conformational isomerism refers to the different spatial arrangements of atoms in a molecule that can be interconverted by rotation around single bonds. In the case of pentane, the rotation around the C-2-C-3 bond leads to various conformers, including staggered and eclipsed forms, which differ in their energy and stability.

Staggered and Eclipsed Conformers

Staggered conformers occur when the substituents on adjacent carbon atoms are positioned as far apart as possible, minimizing steric strain and maximizing stability. In contrast, eclipsed conformers have substituents aligned with each other, leading to increased steric hindrance and higher energy states. Understanding these conformers is crucial for analyzing the stability of pentane's rotational conformations.

Potential Energy Diagram

A potential energy diagram illustrates the energy changes associated with the rotation around a bond, showing the relative stability of staggered versus eclipsed conformers. As the molecule rotates, energy peaks correspond to eclipsed conformers (higher energy) and troughs to staggered conformers (lower energy). This concept helps predict the preferred conformations of pentane based on energy considerations.

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Related Practice

Textbook Question

Draw a Newman projection, similar to Figure 3-25 down the C1—C6 bond in the equatorial conformation of methylcyclohexane. Show that the equatorial methyl group is also anti to C5. (Using your models will help.)

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Textbook Question

Draw Newman projections of the following molecules viewed from the direction of the blue arrows.

(b)

Textbook Question

Draw Newman projections of the following molecules viewed from the direction of the blue arrows.

(a)

Textbook Question

Convert the following Newman projections to skeletal structures and name them.

Textbook Question

Using Newman projections, draw the most stable conformer for each of the following:

b. 3-methylhexane, viewed along the C-3----C-4 bond

Textbook Question

Using Newman projections, draw the most stable conformer for each of the following:

a. 3-methylpentane, viewed along the C-2---C-3 bond

Textbook Question

Draw a potential-energy diagram for rotation about the C-2---C-3 bond of pentane through 360°, starting with the least stable conformer.

Textbook Question

For rotation about the C-3---C-4 bond of 2-methylhexane, do the following:

a. Draw the Newman projection of the most stable conformer.

b. Draw the Newman projection of the least stable conformer.

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