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

25. Condensation Chemistry

Aldol Condensation

Organic Chemistry

25. Condensation Chemistry

Aldol Condensation

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Problem 84

Textbook Question

Biochemists studying the structure of collagen (a fibrous protein in connective tissue) found cross-links containing α,β-unsaturated aldehydes between protein chains. Show the structures of the side chains that react to form these cross-links, and propose a mechanism for their formation in a weakly acidic solution.

Verified step by step guidance

Identify the functional groups involved in the cross-linking reaction. Collagen side chains typically contain lysine residues (with primary amines) and aldehydes. The α,β-unsaturated aldehyde is a conjugated system with a double bond adjacent to the carbonyl group.

Understand the reaction mechanism. In a weakly acidic solution, the primary amine from lysine can act as a nucleophile, attacking the electrophilic carbon of the α,β-unsaturated aldehyde through a Michael addition mechanism.

Propose the first step of the mechanism: Protonation of the carbonyl oxygen of the α,β-unsaturated aldehyde in the weakly acidic environment increases the electrophilicity of the carbonyl carbon, making it more susceptible to nucleophilic attack.

Describe the nucleophilic attack: The amine group from lysine attacks the β-carbon of the α,β-unsaturated aldehyde, forming a new C-N bond. This step results in the formation of an enolate intermediate.

Explain the final step: The enolate intermediate undergoes tautomerization to form a stable imine or Schiff base, completing the cross-linking reaction between the protein chains.

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Key Concepts

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

α,β-Unsaturated Aldehydes

α,β-unsaturated aldehydes are organic compounds that contain a carbonyl group (C=O) adjacent to a double bond (C=C). This structure makes them highly reactive, particularly in nucleophilic addition reactions. In the context of collagen cross-linking, these aldehydes can react with nucleophiles, such as amines from amino acid side chains, to form stable covalent bonds, contributing to the protein's structural integrity.

Cross-Linking in Proteins

Cross-linking refers to the formation of covalent bonds between different protein chains, which enhances the stability and mechanical properties of the protein structure. In collagen, cross-links are crucial for its tensile strength and resilience. The formation of these links often involves reactive side chains of amino acids, such as lysine or proline, which can interact with reactive groups like aldehydes, leading to a network of interconnected fibers.

Mechanism of Aldehyde Reactions

The mechanism of aldehyde reactions typically involves nucleophilic attack on the carbonyl carbon, followed by the formation of a tetrahedral intermediate. In weakly acidic conditions, the protonation of the carbonyl oxygen can enhance the electrophilicity of the carbonyl carbon, facilitating the reaction with nucleophiles. This mechanism is essential for understanding how the side chains of amino acids in collagen can react with α,β-unsaturated aldehydes to form cross-links.

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