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

12. Alcohols, Ethers, Epoxides and Thiols

Leaving Group Conversions - Using HX

Organic Chemistry

12. Alcohols, Ethers, Epoxides and Thiols

Leaving Group Conversions - Using HX

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5:13 minutes

Problem 15

Textbook Question

Neopentyl alcohol, (CH₃)₃CCH₂OH, reacts with concentrated HBr to give 2-bromo-2-methylbutane, a rearranged product. Propose a mechanism for the formation of this product.

Verified step by step guidance

Step 1: Protonation of the hydroxyl group - The reaction begins with the protonation of the hydroxyl group (-OH) in neopentyl alcohol by the concentrated HBr. This forms a good leaving group, water (H2O), and converts the alcohol into a protonated intermediate.

Step 2: Formation of a carbocation - The protonated intermediate undergoes loss of water, resulting in the formation of a primary carbocation at the carbon attached to the hydroxyl group. However, primary carbocations are unstable.

Step 3: Carbocation rearrangement - To achieve greater stability, the primary carbocation undergoes a hydride shift (a hydrogen atom with its bonding electrons moves) from the adjacent tertiary carbon. This rearrangement forms a more stable tertiary carbocation at the central carbon atom.

Step 4: Nucleophilic attack by bromide ion - The bromide ion (Br⁻), which is generated from the dissociation of HBr, acts as a nucleophile and attacks the positively charged tertiary carbocation. This results in the formation of 2-bromo-2-methylbutane.

Step 5: Final product - The final product of the reaction is 2-bromo-2-methylbutane, which is the rearranged product formed through the mechanism involving carbocation rearrangement and nucleophilic substitution.

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Key Concepts

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

Rearrangement in Organic Reactions

Rearrangement refers to the process where the structure of a molecule changes during a chemical reaction, often leading to more stable products. In the case of neopentyl alcohol reacting with HBr, the initial carbocation formed can undergo a hydride shift, resulting in a more stable tertiary carbocation that ultimately leads to the formation of 2-bromo-2-methylbutane.

Carbocation Stability

Carbocations are positively charged carbon species that play a crucial role in many organic reactions. Their stability is influenced by the degree of substitution: tertiary carbocations are more stable than secondary or primary ones due to hyperconjugation and inductive effects. In this reaction, the formation of a tertiary carbocation from neopentyl alcohol is favored, leading to the rearranged product.

SN1 Mechanism

The SN1 mechanism is a two-step nucleophilic substitution process where the first step involves the formation of a carbocation intermediate after the leaving group departs. The second step involves the nucleophile attacking the carbocation. In the case of neopentyl alcohol and HBr, the reaction proceeds via an SN1 mechanism, where the alcohol first loses a water molecule to form a carbocation, which then reacts with bromide to form the final product.

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