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 42a

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

Verified step by step guidance

Step 1: Understand the Newman projection concept. A Newman projection is a way to visualize the conformations of a molecule by looking directly down a specific bond axis. In this case, we are viewing along the C-2-C-3 bond of 3-methylpentane.

Step 2: Identify the substituents attached to the C-2 and C-3 atoms. For 3-methylpentane, C-2 has a hydrogen atom, a methyl group (-CH3), and the rest of the chain (-CH2CH2CH3). C-3 has a hydrogen atom, a methyl group (-CH3), and the rest of the chain (-CH2CH3).

Step 3: Draw the front carbon (C-2) as a circle and place its substituents (hydrogen, methyl group, and chain) at 120° angles around the circle. The back carbon (C-3) is represented as a larger circle behind the front carbon, with its substituents also placed at 120° angles.

Step 4: Arrange the substituents to minimize steric hindrance and achieve the most stable staggered conformation. In a staggered conformation, the substituents on the front and back carbons are positioned as far apart as possible. Place the bulky groups (methyl groups and chains) opposite each other to reduce steric interactions.

Step 5: Verify the stability of the conformer. Ensure that the largest groups (methyl groups and chains) are anti-periplanar (180° apart) to achieve the most stable configuration. Smaller groups like hydrogen atoms can occupy the closer positions (gauche interactions).

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Key Concepts

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

Newman Projections

Newman projections are a way to visualize the conformation of a molecule by looking straight down a bond connecting two carbon atoms. This representation helps in analyzing steric interactions and torsional strain between substituents attached to the carbons. By rotating around the bond, different conformers can be depicted, allowing for the identification of the most stable arrangement.

Conformational Stability

Conformational stability refers to the relative energy of different spatial arrangements of a molecule. Factors influencing stability include steric hindrance, torsional strain, and the presence of electron-donating or withdrawing groups. In the case of 3-methylpentane, the most stable conformer minimizes steric clashes between the bulky methyl group and other hydrogen atoms.

Steric Hindrance

Steric hindrance occurs when atoms or groups within a molecule are in close proximity, leading to repulsive interactions that increase the energy of the system. In conformational analysis, minimizing steric hindrance is crucial for identifying the most stable conformer. For 3-methylpentane, the arrangement that places the methyl group in an equatorial position relative to other substituents typically results in lower steric strain.

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Related Practice

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

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

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

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.

Textbook Question

c. Draw Newman projections of the two conformers of the trans isomer.

d. Which of the conformers predominates at equilibrium?

Textbook Question

Given the following structures, show the Newman projection that would result from looking down the indicated bond in the direction shown. [Orient yourself as if you were the eyeball looking down the bond. Some of the examples have been partially completed for you to fill in the rest.]

(k) <IMAGE>

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Using Newman projections, draw the most stable conformer for each of the following: a. 3-methylpentane, viewed along the C-2---C-3 bond

Key Concepts

Newman Projections

Conformational Stability

Steric Hindrance

Watch next

Using Newman projections, draw the most stable conformer for each of the following:
a. 3-methylpentane, viewed along the C-2---C-3 bond