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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Problem 27

Textbook Question

Imagine an electrophilic addition where the first step is exothermic. Which carbocation—2°, 3°, or neither—would you expect to form preferentially? Explain.

Verified step by step guidance

Begin by understanding the concept of electrophilic addition. This is a reaction where an electrophile reacts with a nucleophile, typically an alkene, to form a carbocation intermediate.

Examine the image provided. It shows two possible pathways for the formation of carbocations: Path A leading to a secondary (2°) carbocation and Path B leading to a tertiary (3°) carbocation.

Note the exothermic nature of the first step, indicated by ΔH < 0. This suggests that the reaction releases energy, favoring the formation of a more stable carbocation.

Consider the stability of carbocations. Tertiary (3°) carbocations are generally more stable than secondary (2°) carbocations due to greater hyperconjugation and inductive effects from surrounding alkyl groups.

Based on the stability preference and the exothermic nature of the reaction, the tertiary (3°) carbocation is expected to form preferentially, as it is more stable and the reaction favors the formation of the most stable intermediate.

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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 reaction mechanism where an electrophile reacts with a nucleophile, typically involving alkenes or alkynes. In this process, the double or triple bond is broken, allowing the electrophile to bond with one of the carbon atoms, leading to the formation of a carbocation intermediate. The stability of the carbocation formed is crucial in determining the reaction pathway and the final product.

Carbocation Stability

Carbocation stability is influenced by the degree of substitution on the positively charged carbon atom. Tertiary (3°) carbocations are more stable than secondary (2°) due to hyperconjugation and inductive effects from surrounding alkyl groups. This stability affects the likelihood of forming a particular carbocation during electrophilic addition reactions, with more stable carbocations being favored in the reaction pathway.

Exothermic Reactions

An exothermic reaction is one that releases energy, usually in the form of heat, during the reaction process. In the context of electrophilic addition, if the first step is exothermic, it suggests that the formation of the carbocation is energetically favorable. This can influence the reaction mechanism, potentially favoring the formation of more stable carbocations, such as tertiary ones, over less stable options.

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Related Practice

Textbook Question

Predict the product(s) that would result when the alkenes shown here are allowed to react under the following conditions: (i) HBr

(g)

Textbook Question

Predict the product(s) that would result when the alkenes shown here are allowed to react under the following conditions:(ii) HCl

(g)

Textbook Question

Predict the product(s) that would result when the alkenes shown here are allowed to react under the following conditions: (i) HBr

(k)

Textbook Question

Predict the product(s) that would result when the alkenes shown here are allowed to react under the following conditions:(ii) HCl

(k)

Textbook Question

At the beginning of Chapter 9, we stated that after finishing Chapters 8 and 9, we would have the ability to make a large variety of functional groups using related reactions. Show the reagent(s) necessary to convert 1-isobutylcyclohexene into the following molecules.

(a)

Textbook Question

Specify the conditions that would allow the synthesis of the 1° and 3° bromoalkanes from the same starting alkene.

Textbook Question

The following haloalkanes can all be prepared starting from the same alkene. Give the alkene and the reagents needed for each.

Textbook Question

Predict the product and provide a mechanism for the reaction of 1-methylcyclohexene with HBr.

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