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

Previous problemNext problem

3:32 minutes

Problem 23a,b

Textbook Question

Choose the member of each pair that will react faster by the S_N1 mechanism.
a. 1-bromopropane or 2-bromopropane
b. 2-bromo-2-methylbutane or 2-bromo-3-methylbutane

Verified step by step guidance

Step 1: Recall the key factors that influence the SN1 mechanism. The SN1 reaction proceeds via a two-step mechanism: (1) formation of a carbocation intermediate and (2) nucleophilic attack on the carbocation. The rate-determining step is the formation of the carbocation, so the stability of the carbocation is the most important factor. More stable carbocations form faster, leading to a faster SN1 reaction.

Step 2: Analyze part (a): Compare 1-bromopropane and 2-bromopropane. When the leaving group (bromine) departs, 1-bromopropane would form a primary carbocation, while 2-bromopropane would form a secondary carbocation. Secondary carbocations are more stable than primary carbocations due to inductive effects and hyperconjugation, so 2-bromopropane will react faster via the SN1 mechanism.

Step 3: Analyze part (b): Compare 2-bromo-2-methylbutane and 2-bromo-3-methylbutane. When the leaving group departs, 2-bromo-2-methylbutane would form a tertiary carbocation, while 2-bromo-3-methylbutane would form a secondary carbocation. Tertiary carbocations are more stable than secondary carbocations due to greater hyperconjugation and inductive effects, so 2-bromo-2-methylbutane will react faster via the SN1 mechanism.

Step 4: Consider other factors that might influence the reaction rate, such as the quality of the leaving group (bromine is a good leaving group in both cases) and the solvent (polar protic solvents favor SN1 reactions). However, in this problem, the carbocation stability is the dominant factor.

Step 5: Summarize the results: For part (a), 2-bromopropane reacts faster via the SN1 mechanism. For part (b), 2-bromo-2-methylbutane reacts faster via the SN1 mechanism. This conclusion is based on the relative stabilities of the carbocations formed in each case.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

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 occurs in two steps: first, the leaving group departs, forming a carbocation intermediate, followed by the nucleophile attacking the carbocation. The rate of the reaction depends primarily on the stability of the carbocation formed. More stable carbocations, such as tertiary or resonance-stabilized ones, will lead to faster reactions.

Carbocation Stability

Carbocation stability is a crucial factor in determining the rate of SN1 reactions. Carbocations are classified as primary, secondary, or tertiary based on the number of alkyl groups attached to the positively charged carbon. Tertiary carbocations are the most stable due to hyperconjugation and inductive effects from surrounding alkyl groups, making them more favorable for SN1 reactions.

Substituent Effects

The presence and position of substituents on the carbon chain can significantly influence the reactivity in SN1 reactions. For example, branching near the reactive center can stabilize the carbocation formed during the reaction. In the given pairs, the structure of the bromopropanes will determine which compound can form a more stable carbocation, thus reacting faster via the SN1 mechanism.

Watch next

Master Drawing the SN1 Mechanism with a bite sized video explanation from Johnny

Start learning

Related Videos

Related Practice

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.

(b)

Textbook Question

Give the S_N1 mechanism for the formation of 2-ethoxy-3-methylbutane, the unrearranged product in this reaction.

Textbook Question

Propose an S_N1 mechanism for the solvolysis of 3-bromo-2,3-dimethylpentane in ethanol.

Textbook Question

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

(a) (CH₃CH₂)₂CH—Cl or (CH₃)₃C—Cl

(b)

Textbook Question

Furfuryl chloride can undergo substitution by both S_N2 and S_N1 mechanisms. Because it is a 1° alkyl halide, we expect S_N2 but not S_N1 reactions. Draw a mechanism for the S_N1 reaction shown below, paying careful attention to the structure of the intermediate. How can this primary halide undergo S_N1 reactions?