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

4. Alkanes and Cycloalkanes

Naming Alkenes

Organic Chemistry

4. Alkanes and Cycloalkanes

Naming Alkenes

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3:05 minutes

Problem 2a

Textbook Question

For each molecular formula, draw all the isomeric alkynes, and give their IUPAC names. Circle the acetylenic hydrogen of each terminal alkyne.
(a) C₅H₈ (three isomers)

Verified step by step guidance

Step 1: Understand the concept of isomerism. Isomers are compounds with the same molecular formula but different structural arrangements. In this case, we are looking for structural isomers of alkynes with the formula C5H8.

Step 2: Recall that alkynes are hydrocarbons containing a carbon-carbon triple bond. The simplest alkyne is ethyne (acetylene), and terminal alkynes have the triple bond at the end of the carbon chain, which includes an acetylenic hydrogen.

Step 3: Begin by drawing the longest carbon chain possible with a triple bond. For C5H8, start with a five-carbon chain and place the triple bond between the first and second carbon atoms to form 1-pentyne. This is a terminal alkyne, so circle the hydrogen attached to the first carbon.

Step 4: Next, consider moving the triple bond to different positions along the carbon chain. Place the triple bond between the second and third carbon atoms to form 2-pentyne. This is an internal alkyne, so it does not have an acetylenic hydrogen to circle.

Step 5: Finally, explore branching possibilities. Create a four-carbon chain with a methyl group attached, and place the triple bond at the end to form 3-methyl-1-butyne. This is another terminal alkyne, so circle the hydrogen attached to the first carbon.

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Key Concepts

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

Isomerism in Organic Chemistry

Isomerism refers to the phenomenon where compounds have the same molecular formula but different structural arrangements. In the context of alkynes, structural isomers can differ in the position of the triple bond or the branching of the carbon chain. Understanding isomerism is crucial for identifying and drawing all possible isomeric structures for a given molecular formula.

Alkynes and Terminal Alkynes

Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond. Terminal alkynes have the triple bond at the end of the carbon chain, which results in the presence of an acetylenic hydrogen atom. This hydrogen is unique because it is directly bonded to a carbon atom involved in a triple bond, making it more acidic than hydrogens in alkanes or alkenes.

IUPAC Nomenclature for Alkynes

The IUPAC naming system provides a standardized way to name organic compounds. For alkynes, the longest carbon chain containing the triple bond is identified, and the chain is numbered to give the lowest possible number to the triple bond. The suffix '-yne' is used to indicate the presence of a triple bond, and any substituents are named and numbered accordingly. This systematic approach ensures clarity and consistency in chemical communication.

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