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

Chirality

Organic Chemistry

5. Chirality

Chirality

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2:24 minutes

Problem 25

Textbook Question

The chiral BINAP ligand shown in Figure 8-8 contains no asymmetric carbon atoms. Explain how this ligand is chiral.

Verified step by step guidance

The BINAP ligand is chiral due to its axial chirality, which arises from the spatial arrangement of the two naphthyl groups connected to the phosphorus atoms. These groups are twisted relative to each other, creating a non-superimposable mirror image.

Unlike traditional chirality that involves asymmetric carbon atoms, axial chirality is a result of restricted rotation around a bond, leading to a fixed spatial arrangement of substituents.

In the BINAP ligand, the bulky naphthyl groups prevent free rotation around the bond connecting them to the phosphorus atoms, locking the molecule into a specific chiral conformation.

The chirality of BINAP is crucial in asymmetric catalysis, as it allows the ligand to induce stereoselectivity in reactions, such as the hydrogenation shown in the figure, where the Ru(BINAP)Cl₂ catalyst produces the (R)-enantiomer with high enantiomeric excess (96% e.e.).

The structure of BINAP demonstrates that chirality can exist without asymmetric carbon atoms, broadening the understanding of stereochemistry in organic molecules and catalysts.

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Key Concepts

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

Chirality

Chirality refers to the geometric property of a molecule that makes it non-superimposable on its mirror image, akin to how left and right hands are distinct. A molecule can be chiral even without asymmetric carbon atoms if it has a specific spatial arrangement that creates two non-superimposable forms, known as enantiomers. This is crucial in understanding how certain ligands, like BINAP, can exhibit chirality through their overall three-dimensional structure.

BINAP Ligand

BINAP (1,1'-bi-2-naphthol) is a bidentate ligand commonly used in asymmetric catalysis. It features two naphthalene rings connected by a single bond, allowing it to coordinate to metal centers, such as ruthenium in the provided example. The unique arrangement of its substituents can create a chiral environment around the metal, facilitating selective reactions that produce specific enantiomers.

Asymmetric Catalysis

Asymmetric catalysis is a process where a catalyst induces the formation of one enantiomer over another in a chemical reaction. This is particularly important in organic synthesis, as it allows for the production of chiral molecules with high enantiomeric excess (e.e.). The use of chiral ligands like BINAP in conjunction with transition metals enables chemists to achieve high selectivity in reactions, as seen in the hydrogenation example provided.