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

5. Chirality

Optical Activity

Organic Chemistry

5. Chirality

Optical Activity

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1:47 minutes

Problem 28

Textbook Question

Based on the absolute configuration of (S)-butan-2-ol, what can you say about the direction it rotates plane-polarized light?

Verified step by step guidance

Step 1: Understand the relationship between absolute configuration and optical activity. The absolute configuration (R or S) of a chiral molecule does not directly determine the direction (dextrorotatory or levorotatory) in which it rotates plane-polarized light.

Step 2: Recall that the direction of rotation of plane-polarized light (optical activity) is an experimental property and is denoted as (+) for dextrorotatory (clockwise) or (-) for levorotatory (counterclockwise). This property must be determined experimentally.

Step 3: Note that (S)-butan-2-ol has the absolute configuration 'S', but this does not imply whether it is (+) or (-). For example, (S)-butan-2-ol is known to rotate plane-polarized light in the counterclockwise direction, making it levorotatory (-).

Step 4: Emphasize that the correlation between absolute configuration and optical rotation is specific to each compound and cannot be generalized. Experimental data is required to determine the optical rotation.

Step 5: Conclude that while the absolute configuration of (S)-butan-2-ol is known, its optical rotation direction (counterclockwise, or levorotatory) must be experimentally verified and is not inherently linked to the 'S' configuration.

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Key Concepts

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

Optical Activity

Optical activity refers to the ability of chiral compounds to rotate the plane of polarized light. This property arises from the asymmetry in the molecular structure, which allows chiral molecules to interact differently with light. The direction of rotation can be either clockwise (dextrorotatory) or counterclockwise (levorotatory), and is denoted by the symbols '+' or '−'.

Absolute Configuration

Absolute configuration describes the spatial arrangement of atoms in a chiral molecule, designated as either 'R' (rectus) or 'S' (sinister) based on the Cahn-Ingold-Prelog priority rules. For (S)-butan-2-ol, the 'S' configuration indicates a specific three-dimensional arrangement of its substituents around the chiral center, which influences its optical activity.

Chirality and Stereoisomers

Chirality is a property of a molecule that makes it non-superimposable on its mirror image, leading to the existence of stereoisomers. These stereoisomers, such as (R)- and (S)- forms of butan-2-ol, can exhibit different physical properties, including the direction in which they rotate polarized light. Understanding chirality is crucial for predicting the behavior of organic compounds in optical activity.

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Related Practice

Textbook Question

a. Is (R)-lactic acid dextrorotatory or levorotatory?

b. Is (R)-sodium lactate dextrorotatory or levorotatory?

Textbook Question

Which of the following are optically active?

Textbook Question

Which stereoisomers are optically inactive?

Textbook Question

Make a model of each compound, draw it in its most symmetric conformation, and determine whether it is capable of showing optical activity.

a. 1-bromo-1-chloroethane

b. 1-bromo-2-chloroethane

Textbook Question

Naproxen is a commercially available anti-inflammatory sold under the name Aleve.

(b) Given that naproxen rotates plane-polarized light in the clockwise direction, should it be referred to as (d) or (l)?

(d) What direction (d or l; + or −) would you expect the enantiomer of naproxen to rotate plane-polarized light?

Textbook Question

When the following substituted biphenyl was synthesized, it was found to have a specific rotation [α] of -23° at 25°C . When the specific rotation was measured at 100°C the compound had a specific rotation of 0° . Upon cooling back to 25°C the specific rotation was measured again, resulting in [α] = 0°. Explain these results.

Textbook Question

(R)-Limonene is a cyclic terpene responsible for the smell of oranges and other citrus fruits.

(a) Given that (R)-limonene rotates plane-polarized light in the clockwise direction, should it be referred to as (d) or (l)?

(b) Is it (+) or (-)?

Textbook Question

Which of the following diastereomers of hexane-2,5-diol is optically inactive? Why?

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