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

10. Addition Reactions

Hydrohalogenation

Organic Chemistry

10. Addition Reactions

Hydrohalogenation

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2:08 minutes

Problem 62a

Textbook Question

When 3-methyl-1-butene reacts with HBr, two alkyl halides are formed: 2-bromo-3-methylbutane and 2-bromo-2-methylbutane. Propose a mechanism that explains the formation of these two products.

Verified step by step guidance

Step 1: Begin by identifying the structure of 3-methyl-1-butene. It is an alkene with a double bond between the first and second carbons, and a methyl group attached to the third carbon. The molecular formula is C5H10.

Step 2: Recognize that the reaction involves the addition of HBr to the alkene. This is an electrophilic addition reaction, where the π-electrons of the double bond act as a nucleophile and attack the electrophilic hydrogen (H) of HBr.

Step 3: The first step of the mechanism involves protonation of the double bond. The π-electrons of the double bond attack the hydrogen atom of HBr, leading to the formation of a carbocation intermediate. Depending on which carbon of the double bond gets protonated, two possible carbocations can form: a secondary carbocation at C2 or a tertiary carbocation at C3.

Step 4: Analyze the stability of the carbocations. The tertiary carbocation at C3 is more stable due to hyperconjugation and inductive effects from the methyl groups. However, the secondary carbocation at C2 can also form, albeit less favorably. Both intermediates are possible, leading to two different products.

Step 5: In the final step, the bromide ion (Br⁻), which is the nucleophile, attacks the carbocation. If the secondary carbocation at C2 is attacked, the product is 2-bromo-3-methylbutane. If the tertiary carbocation at C3 is attacked, the product is 2-bromo-2-methylbutane. This explains the formation of the two alkyl halides.

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Key Concepts

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

Electrophilic Addition

Electrophilic addition is a fundamental reaction mechanism in organic chemistry where an electrophile reacts with a nucleophile, leading to the formation of a more saturated compound. In the case of alkenes like 3-methyl-1-butene, the double bond acts as a nucleophile, attacking the electrophilic hydrogen in HBr, resulting in the formation of a carbocation intermediate.

Carbocation Stability

Carbocation stability is crucial in determining the outcome of reactions involving carbocations. Tertiary carbocations are more stable than secondary or primary ones due to hyperconjugation and inductive effects. In the reaction of 3-methyl-1-butene with HBr, the formation of a more stable carbocation leads to the preferential formation of certain alkyl halides, such as 2-bromo-2-methylbutane.

Markovnikov's Rule

Markovnikov's Rule states that in the addition of HX to an alkene, the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms already attached. This rule helps predict the major product in electrophilic addition reactions. In this case, the addition of HBr to 3-methyl-1-butene results in the formation of 2-bromo-3-methylbutane and 2-bromo-2-methylbutane, illustrating the application of this rule.

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