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

7. Substitution Reactions

SN1 Reaction

Organic Chemistry

7. Substitution Reactions

SN1 Reaction

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5:06 minutes

Problem 23c,d

Textbook Question

Choose the member of each pair that will react faster by the SN1 mechanism.
c. n-propyl bromide or allyl bromide
d. 1-bromo-2,2-dimethylpropane or 2-bromopropane

Verified step by step guidance

Step 1: Recall the key factors that influence the SN1 reaction rate. The SN1 mechanism involves the formation of a carbocation intermediate, so the stability of the carbocation is the most critical factor. More stable carbocations form faster, leading to a faster reaction.

Step 2: Analyze the first pair: n-propyl bromide and allyl bromide. When n-propyl bromide undergoes ionization, it forms a primary carbocation, which is relatively unstable. In contrast, allyl bromide forms an allylic carbocation, which is stabilized by resonance. Resonance stabilization makes the allylic carbocation much more stable than the primary carbocation.

Step 3: Conclude for the first pair: Since the allylic carbocation is more stable due to resonance, allyl bromide will react faster via the SN1 mechanism compared to n-propyl bromide.

Step 4: Analyze the second pair: 1-bromo-2,2-dimethylpropane and 2-bromopropane. When 1-bromo-2,2-dimethylpropane ionizes, it forms a tertiary carbocation, which is highly stable due to inductive effects and hyperconjugation from the surrounding alkyl groups. On the other hand, 2-bromopropane forms a secondary carbocation, which is less stable than a tertiary carbocation.

Step 5: Conclude for the second pair: Since the tertiary carbocation formed by 1-bromo-2,2-dimethylpropane is more stable, it will react faster via the SN1 mechanism compared to 2-bromopropane.

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Key Concepts

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

SN1 Mechanism

The SN1 mechanism is a type of nucleophilic substitution reaction that proceeds in two steps: the formation of a carbocation intermediate followed by nucleophilic attack. The rate of the reaction depends primarily on the stability of the carbocation formed. More stable carbocations, such as tertiary or allylic ones, will lead to faster reactions.

Carbocation Stability

Carbocation stability is crucial in determining the rate of SN1 reactions. Carbocations are stabilized by hyperconjugation and inductive effects from adjacent alkyl groups. Tertiary carbocations are the most stable, followed by secondary and primary. Allylic carbocations, which can delocalize charge through resonance, are also relatively stable.

Substituent Effects

The nature of substituents on the carbon atom bearing the leaving group influences the reaction rate. Electron-donating groups can stabilize the carbocation, while steric hindrance can impede the formation of the carbocation. In the context of the given pairs, the structure of the alkyl groups attached to the leaving group (bromide) will determine which compound reacts faster via the SN1 mechanism.

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Related Practice

Textbook Question

Which compound is more reactive in an S_N1 reaction? In each case, you can assume that both alkyl halides have the same stability.

Textbook Question

a. Assuming that the two compounds shown below have the same stability, which one would you expect to be more reactive in an S_N1 reaction?

b. Draw the products that each would form when the solvent is ethanol.

Textbook Question

A reluctant first-order substrate can be forced to ionize by adding some silver nitrate (one of the few soluble silver salts) to the reaction. Silver ion reacts with the halogen to form a silver halide (a highly exothermic reaction), generating the cation of the alkyl group.

Give mechanisms for the following silver-promoted rearrangements.

(b)

Textbook Question

Propose a mechanism involving a hydride shift or an alkyl shift for each solvolysis reaction. Explain how each rearrangement forms a more stable intermediate.

Hint: Most rearrangements convert 2° (or incipient 1°) carbocations to 3° or resonance-stabilized carbocations.

(c)

Textbook Question

Predict the compound in each pair that will undergo solvolysis (in aqueous ethanol) more rapidly.

(c)

(d)

Textbook Question

Allylic halides have the structure

a. Show how the first-order ionization of an allylic halide leads to a resonance-stabilized cation.

Textbook Question

Often, compounds can be synthesized by more than one method. Show how this 3° alcohol can be made from the following:

(d) a 3° alkyl bromide

Textbook Question

Give the substitution products expected from solvolysis of each compound by heating in ethanol.

(c)

(d)

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Choose the member of each pair that will react faster by the SN1 mechanism.c. n-propyl bromide or allyl bromided. 1-bromo-2,2-dimethylpropane or 2-bromopropane

Key Concepts

SN1 Mechanism

Carbocation Stability

Substituent Effects

Watch next

Choose the member of each pair that will react faster by the SN1 mechanism.
c. n-propyl bromide or allyl bromide
d. 1-bromo-2,2-dimethylpropane or 2-bromopropane