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

16. Conjugated Systems

Conjugation Chemistry

Organic Chemistry

16. Conjugated Systems

Conjugation Chemistry

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Problem 18a

Textbook Question

For the following terpenes, identify the isoprene units. In cross-linked or ring-containing terpenes, linkages can be formed between more than just C₁ and C₄ of isoprene.
(a)

Verified step by step guidance

Step 1: Recall the structure of an isoprene unit, which consists of a five-carbon chain with two double bonds (C5H8). The carbons are numbered as follows: C1 and C4 are the terminal carbons, and C2, C3, and C5 are internal carbons.

Step 2: Analyze the structure of citronellal provided in the image. Citronellal is a monoterpene, meaning it is composed of two isoprene units (C10H16). Look for repeating patterns of five-carbon units within the molecule.

Step 3: Identify the first isoprene unit. In citronellal, the first isoprene unit can be traced starting from the methyl group (CH3) attached to the double bond and extending to the adjacent carbons, including the double bond itself.

Step 4: Identify the second isoprene unit. The second isoprene unit begins at the carbon connected to the aldehyde group (CHO) and extends through the chain, including the branching methyl group and the remaining carbons.

Step 5: Note that the linkage between the two isoprene units in citronellal is not a simple C1-C4 connection. Instead, the molecule exhibits a more complex arrangement due to the presence of branching and functional groups, which is common in terpenes with cross-linked or ring-containing structures.

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Key Concepts

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

Isoprene Unit

Isoprene units are the fundamental building blocks of terpenes, consisting of a five-carbon structure with the formula C5H8. Terpenes are formed by the polymerization of isoprene units, which can be linked in various ways to create diverse structures. Understanding how these units combine is essential for identifying the structure and classification of terpenes.

Terpene Structure

Terpenes are a large class of organic compounds produced by many plants, characterized by their strong odors and roles in plant defense. They can be linear or cyclic, and their structures can vary significantly based on how the isoprene units are arranged and linked. Recognizing the structural variations helps in identifying specific terpenes and their properties.

Cross-linking in Terpenes

Cross-linking in terpenes refers to the formation of bonds between different isoprene units beyond the typical C1 and C4 positions. This can lead to complex structures such as rings or branched chains, which significantly influence the chemical properties and biological functions of the terpenes. Understanding cross-linking is crucial for analyzing the structure of terpenes like citronellal.

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Related Practice

Textbook Question

Identify the isoprene units in the terpenes shown. In cross-linked or ring-containing terpenes, linkages can be formed between more than just C₁ and C₄ of isoprene.

(b)

Textbook Question

Identify the isoprene units in the terpenes shown. In cross-linked or ring-containing terpenes, linkages can be formed between more than just C₁ and C₄ of isoprene.

(c)

Textbook Question

Identify the isoprene units in the terpenes shown. In cross-linked or ring-containing terpenes, linkages can be formed between more than just C₁ and C₄ of isoprene.

(e)

Textbook Question

Vitamin E, especially the B ring and the side chain, is a terpenoid derivative. Identify the isoprene units nature used to make it.

Textbook Question

For the following terpenes, identify the isoprene units. In cross-linked or ring-containing terpenes, linkages can be formed between more than just C₁ and C₄ of isoprene.

(d)

Textbook Question

North American termite soldiers, when encountering enemy insects, contract their mandibular muscles, expelling a mixture of chemicals that essentially trap their enemies in a glue-like substance. This weapon, built into the face of the termite, is called the fontanellar gun. It releases a mixture of pinene (62%), myrcene (27%), and limonene (11%).

(b) Suggest an acid-catalyzed mechanism by which pinene could be produced from limonene.

Textbook Question

Identify the following dienes as being in the s-cis or s-trans conformation. If they are in the s-trans conformation, draw them in the s-cis conformation. [It may not always be possible.]

(c)

Textbook Question

Identify the following dienes as being in the s-cis or s-trans conformation. If they are in the s-trans conformation, draw them in the s-cis conformation. [It may not always be possible.]

(e)

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For the following terpenes, identify the isoprene units. In cross-linked or ring-containing terpenes, linkages can be formed between more than just C1 and C4 of isoprene.(a)

Key Concepts

Isoprene Unit

Terpene Structure

Cross-linking in Terpenes

Watch next

For the following terpenes, identify the isoprene units. In cross-linked or ring-containing terpenes, linkages can be formed between more than just C₁ and C₄ of isoprene.
(a)