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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6:08 minutes

Problem 43(2)

Textbook Question

a. Starting with 3-methyl-1-butyne, how can you prepare the following alcohols?
2. 3-methyl-1-butanol
b. In each case, a second alcohol would also be obtained. What alcohol would it be?

Verified step by step guidance

Step 1: Analyze the starting material, 3-methyl-1-butyne, which is a terminal alkyne. To convert it into an alcohol, consider the addition of water across the triple bond (hydration reaction).

Step 2: Use hydroboration-oxidation to achieve anti-Markovnikov addition of water. This involves two steps: (1) React 3-methyl-1-butyne with BH₃ (borane) or a borane derivative like 9-BBN to form an organoborane intermediate. (2) Oxidize the intermediate with H₂O₂ (hydrogen peroxide) in a basic solution (NaOH) to yield 3-methyl-1-butanol.

Step 3: Recognize that hydroboration-oxidation produces the anti-Markovnikov alcohol as the major product. However, a second alcohol can form as a minor product due to Markovnikov hydration. To achieve this, use acid-catalyzed hydration (H₂SO₄ and H₂O) in the presence of HgSO₄ (mercuric sulfate) as a catalyst.

Step 4: Acid-catalyzed hydration adds water across the triple bond in a Markovnikov manner, forming an enol intermediate. This enol tautomerizes to a ketone, which can then be reduced to form a secondary alcohol. The secondary alcohol in this case would be 3-methyl-2-butanol.

Step 5: Summarize the two alcohols obtained: (1) 3-methyl-1-butanol (anti-Markovnikov product from hydroboration-oxidation) and (2) 3-methyl-2-butanol (Markovnikov product from acid-catalyzed hydration followed by reduction).

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Key Concepts

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

Alkyne Hydroboration-Oxidation

Hydroboration-oxidation is a two-step reaction used to convert alkynes into alcohols. In the first step, the alkyne reacts with diborane (B2H6) to form an organoborane intermediate. The second step involves oxidation with hydrogen peroxide (H2O2) and sodium hydroxide (NaOH), resulting in the formation of an alcohol. This method is particularly useful for synthesizing alcohols with specific stereochemistry.

Markovnikov's Rule

Markovnikov's Rule states that when HX (where X is a halogen or OH) adds to an alkene or alkyne, the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms already attached. This principle helps predict the major product of the reaction, guiding the synthesis of specific alcohols from alkynes by determining the regioselectivity of the addition reactions.

Rearrangement Reactions

Rearrangement reactions involve the structural reorganization of a molecule to form a more stable product. In the context of alcohol synthesis from alkynes, these reactions can lead to the formation of different alcohols, including secondary or tertiary alcohols, depending on the stability of the carbocation intermediates formed during the reaction. Understanding these rearrangements is crucial for predicting the outcome of the synthesis.

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Textbook Question

For each of the following target molecules, design a multistep synthesis to show how it can be prepared from the given starting material:

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A, a compound with molecular formula C₆H₁₀, contains three methylene units. A reacts with one equivalent of H₂ over Pd/C to yield B. A reacts with aqueous acid to form a single product, C, and undergoes hydroboration/oxidation to form a pair of enantiomers, D and E. Ozonolysis of A followed by reaction with dimethyl sulfide forms F with molecular formula C₆H₁₀O₂. Provide structures for A–F.

Textbook Question

Starting with cyclohexene, how can the following compounds be prepared?

c. dicyclohexyl ether

Textbook Question

Fill in each box with the appropriate reagent:

Textbook Question

Write the appropriate reagent over each arrow.

Textbook Question

Using hex-1-ene as your starting material, show how you would synthesize the following compounds. (Once you have shown how to synthesize a compound, you may use it as the starting material in any later parts of this problem.)

d. hex-2-yne

e. hexan-2-one

f. hexanal

Textbook Question

g. pentanoic acid

h. pentanal

i. undec-6-yn-5-ol

Textbook Question

Show how you would accomplish the following synthetic transformations. Show all intermediates.

d. trans-hex-2-ene → hex-2-yne

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