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

14. Synthetic Techniques

Retrosynthesis

Organic Chemistry

14. Synthetic Techniques

Retrosynthesis

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4:42 minutes

Problem 38

Textbook Question

a. Propose a mechanism for the following reaction.
2 (CH₃)₂C=CH–CH₃ + cat. H⁺ → 2,3,4,4-tetramethylhex-2-ene
b. Show the first three steps (as far as the tetramer) in the BF₃–catalyzed polymerization of propylene to form polypropylene.

Verified step by step guidance

Step 1: For part (a), begin by identifying the reaction type. The reaction involves the acid-catalyzed dimerization of 2-methyl-2-pentene ((CH3)2C=CH-CH3). The mechanism starts with protonation of the double bond by the acid catalyst (H+), forming a carbocation intermediate. Write the protonation step as:

(CH 3) 2 C = CH - CH 3 + H + \to (CH 3) 2 C - CH - CH 3 +

Step 2: The carbocation formed in step 1 undergoes a nucleophilic attack by another molecule of 2-methyl-2-pentene. This forms a new bond between the two molecules, resulting in a larger carbocation intermediate. Represent this step as:

(CH 3) 2 C - CH - CH 3 + + (CH 3) 2 C = CH - CH 3 \to (CH 3) 2 C - CH - C (CH 3) 2 - CH 3 +

Step 3: The carbocation intermediate formed in step 2 undergoes deprotonation to form the final product, 2,3,4,4-tetramethylhex-2-ene. This step involves the removal of a proton from the carbocation, restoring the double bond. Write this step as:

(CH 3) 2 C - CH - C (CH 3) 2 - CH 3 + \to (CH 3) 2 C = C (CH 3) 2 - CH 3

Step 4: For part (b), the BF3-catalyzed polymerization of propylene begins with the formation of a complex between BF3 and propylene. BF3 acts as a Lewis acid, accepting electrons from the double bond of propylene to form a carbocation intermediate. Represent this step as:

CH 2 = CH CH 3 + BF 3 \to CH 2 - CH CH 3 +

Step 5: The carbocation formed in step 4 reacts with another molecule of propylene, initiating chain growth. This forms a larger carbocation intermediate. Represent this step as:

CH 2 - CH CH 3 + + CH 2 = CH CH 3 \to CH 2 - CH CH 3 - CH 2 - CH CH 3 +

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Key Concepts

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

Reaction Mechanism

A reaction mechanism is a step-by-step description of the process by which reactants are converted into products. It outlines the individual steps, including bond breaking and formation, and the intermediates formed during the reaction. Understanding mechanisms is crucial for predicting the outcome of chemical reactions and for designing new synthetic pathways.

Catalysis

Catalysis involves the acceleration of a chemical reaction by a substance called a catalyst, which is not consumed in the reaction. In the context of the given question, H+ and BF3 serve as catalysts that facilitate the reactions without altering their own chemical structure. Catalysts lower the activation energy required for reactions, making them proceed more rapidly and efficiently.

Polymerization

Polymerization is the process by which small molecules, known as monomers, chemically bond to form a larger, more complex structure called a polymer. In the case of propylene, the polymerization process involves the formation of long chains through repeated addition reactions. Understanding the steps of polymerization is essential for predicting the properties and applications of the resulting polymer, such as polypropylene.

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Textbook Question

Show how you would synthesize the following compounds. As starting materials, you may use any alcohols containing four or fewer carbon atoms, cyclohexanol, and any necessary solvents and inorganic reagents.

(h)

Textbook Question

Show how you would synthesize the following compound. As starting materials, you may use any alcohols containing five or fewer carbon atoms and any necessary solvents and inorganic reagents.

Textbook Question

When doing synthesis, you will often find yourself repeating the same series of steps. To see this in action, synthesize the following aldehydes beginning with an organic molecule containing three carbons or fewer.

(b)

Textbook Question

Suggest a synthetic scheme, involving a protecting group, to generate the molecule shown starting with the molecule at the left.

(a)

Textbook Question

Develop syntheses for the following compounds, using acetylene and compounds containing no more than four carbon atoms as your organic starting materials.

(a) 3-methylnon-4-yn-3-ol (“3-ol” means there is an OH group on C3.)

Textbook Question

Develop syntheses for the following compounds, using acetylene and compounds containing no more than four carbon atoms as your organic starting materials.

(b) cis-1-ethyl-2-methylcyclopropane

Textbook Question

Propose mechanisms to explain the opposite regiochemistry observed in the following two reactions.

Textbook Question

Show how you would accomplish the following synthetic conversions.

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