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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4:45 minutes

Problem 42c

Textbook Question

Using Newman projections, draw the most stable conformer for each of the following:
c. 3,3-dimethylhexane, viewed along the C-3---C-4 bond

Verified step by step guidance

Identify the structure of 3,3-dimethylhexane. The molecule has a hexane backbone with two methyl groups attached to the third carbon. The task is to analyze the conformation along the C-3 to C-4 bond.

Draw the Newman projection template for the C-3 to C-4 bond. Place the C-3 carbon at the front (circle) and the C-4 carbon at the back (larger circle). Attach the substituents to each carbon based on their connectivity in the molecule.

For the front carbon (C-3), attach two methyl groups (from the 3,3-dimethyl substitution) and one hydrogen. For the back carbon (C-4), attach two hydrogens and one ethyl group (representing the rest of the hexane chain).

To determine the most stable conformer, arrange the substituents to minimize steric hindrance. Place the bulky groups (the two methyl groups on C-3 and the ethyl group on C-4) as far apart as possible. This typically corresponds to a staggered conformation where the largest groups are anti to each other.

Redraw the Newman projection with the optimized staggered conformation. Verify that the bulky groups are positioned to minimize steric interactions, ensuring the most stable conformer is represented.

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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 the bond connecting two carbon atoms. This representation helps in analyzing steric interactions and torsional strain between substituents attached to the carbons, allowing chemists to identify the most stable conformers based on the spatial arrangement of these groups.

Conformational Stability

Conformational stability refers to the relative energy of different spatial arrangements of a molecule. In the case of alkanes, steric hindrance and torsional strain play significant roles in determining which conformer is most stable. Generally, staggered conformations are more stable than eclipsed ones due to minimized repulsion between electron clouds of substituents.

Steric Hindrance

Steric hindrance occurs when atoms or groups within a molecule are forced close together, leading to increased repulsion and higher energy states. In the context of 3,3-dimethylhexane, the bulky methyl groups can create significant steric interactions, influencing the stability of different conformers. Understanding this concept is crucial for predicting which conformer will be the most stable.

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Related Practice

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.]

(b) <IMAGE>

Textbook Question

Looking down the indicated bond, show the three most stable conformations and choose the one that is most stable. Be sure that the first Newman projection you show is the one you see initially (before rotation). [Why should none of your three Newman projections show eclipsed conformations?]

(b) <IMAGE>

Textbook Question

For each of the following structures, which staggered Newman projection skeleton from Assessment 3.51 should you draw first to show what is seen when looking down the indicated bond?

(d) <IMAGE>

Textbook Question

Convert each Newman projection to the equivalent line–angle formula, and assign the IUPAC name.

(c)

(d)

Textbook Question

For the following molecule, draw the Newman projection (around the 2,3-bond) with a dihedral angle of 180° between the bromine and hydrogen.

Textbook Question

Conformational studies on ethane-1,2-diol (HOCH₂–CH₂OH) have shown the most stable conformation about the central C―C bond to be the gauche conformation, which is 9.6 kJ/mol (2.3 kcal/mol) more stable than the anti conformation. Draw Newman projections of these conformers, and explain this curious result.

Textbook Question

Draw the conformer that is present in greatest concentration.

Textbook Question

(e) <IMAGE>

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