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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Problem 26

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 (-)?
(c) What direction (d or l; + or −) would you expect (S)-limonene to rotate plane-polarized light?

Verified step by step guidance

Step 1: Understand the relationship between the (R) and (S) stereochemical designations and the direction of rotation of plane-polarized light. The (R) and (S) designations are based on the Cahn-Ingold-Prelog priority rules and do not directly indicate the direction of optical rotation.

Step 2: Recall that the terms (d) and (l) refer to dextrorotatory and levorotatory, respectively. A compound is dextrorotatory (d) if it rotates plane-polarized light clockwise, and levorotatory (l) if it rotates plane-polarized light counterclockwise. Since (R)-limonene rotates light clockwise, it should be referred to as (d).

Step 3: Understand the relationship between the (+) and (−) notation and optical rotation. The (+) notation corresponds to clockwise rotation (dextrorotatory), while the (−) notation corresponds to counterclockwise rotation (levorotatory). Since (R)-limonene rotates light clockwise, it is also (+).

Step 4: Consider the stereochemical inversion from (R)-limonene to (S)-limonene. The (S)-enantiomer of a chiral compound typically rotates plane-polarized light in the opposite direction to its (R)-enantiomer. Therefore, if (R)-limonene is (d) and (+), (S)-limonene would be (l) and (−).

Step 5: Summarize the findings: (a) (R)-limonene is (d), (b) (R)-limonene is (+), and (c) (S)-limonene is expected to be (l) and (−), as it rotates plane-polarized light in the opposite direction to (R)-limonene.

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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 of the molecule, which can exist in two enantiomeric forms that rotate light in opposite directions. The direction of rotation is designated as clockwise (dextrorotatory, +) or counterclockwise (levorotatory, -). Understanding optical activity is crucial for distinguishing between enantiomers.

Enantiomers and Chirality

Enantiomers are pairs of molecules that are non-superimposable mirror images of each other, typically due to the presence of a chiral center. Chirality is a key concept in organic chemistry, as it affects the physical and chemical properties of compounds, including their interaction with polarized light. The designation of enantiomers as (R) or (S) is based on the Cahn-Ingold-Prelog priority rules, which help determine their spatial arrangement.

Cahn-Ingold-Prelog System

The Cahn-Ingold-Prelog (CIP) system is a set of rules used to assign the configuration of chiral centers in molecules. It involves ranking the substituents attached to the chiral carbon based on atomic number and connectivity. The configuration is designated as (R) for clockwise and (S) for counterclockwise arrangement when viewed from a specific perspective. This system is essential for accurately describing the stereochemistry of organic compounds.

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Related Practice

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

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

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

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

Textbook Question

Draw the structure for a compound with molecular formula C₂H₂I₂F₂

c. that is optically active.

Textbook Question

A solution of 0.50 g of (−)-epinephrine (see Figure 5-16) dissolved in 10.0 mL of dilute aqueous HCl was placed in a 20-cm polarimeter tube. Using the sodium D line, the rotation was found to be −5.1° at 25 °C. Determine the specific rotation of epinephrine.

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Textbook Question

Calculate the specific rotations of the following samples taken at 25 °C using the sodium D line.

a. 1.00 g of sample is dissolved in 20.0 mL of ethanol. Then 5.00 mL of this solution is placed in a 20.0-cm polarimeter tube. The observed rotation is 1.25° counterclockwise.

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