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

8. Elimination Reactions

SN1 SN2 E1 E2 Chart (Big Daddy Flowchart)

Organic Chemistry

8. Elimination Reactions

SN1 SN2 E1 E2 Chart (Big Daddy Flowchart)

Previous problemNext problem

Problem 15a

Textbook Question

Which of the following S_N2 and E2 reactions, respectively, is faster? Justify your choice.
(a)

Verified step by step guidance

Step 1: Analyze the reaction conditions for each case. In the first reaction, NaOH is used as the nucleophile in an aqueous solution, which promotes an SN2 mechanism due to the strong nucleophilicity of OH⁻. In the second reaction, H₂O acts as the nucleophile, which is weaker and favors an SN1 mechanism rather than SN2.

Step 2: Consider the substrate structure. Both reactions involve a primary alkyl bromide (CH₃CH₂Br), which is highly favorable for SN2 reactions due to minimal steric hindrance around the electrophilic carbon.

Step 3: Compare the nucleophiles. OH⁻ is a stronger nucleophile than H₂O because it is negatively charged and more reactive. This makes the first reaction faster under SN2 conditions.

Step 4: Evaluate the solvent effects. The first reaction occurs in a polar aprotic environment (NaOH in H₂O), which enhances the nucleophilicity of OH⁻ and accelerates the SN2 reaction. The second reaction occurs in a polar protic solvent (H₂O), which stabilizes the nucleophile and slows down the SN2 reaction.

Step 5: Conclude that the first reaction (NaOH in H₂O) is faster for the SN2 mechanism due to the stronger nucleophile and favorable reaction conditions. For E2 reactions, the analysis would depend on the presence of a strong base and the substrate's ability to undergo elimination, which is not explicitly shown in the given problem.

Verified video answer for a similar problem:

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

Play a video:

Was this helpful?

Key Concepts

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

SN2 Reactions

SN2 (Substitution Nucleophilic Bimolecular) reactions involve a nucleophile attacking an electrophile in a single concerted step, resulting in the displacement of a leaving group. The reaction rate depends on the concentration of both the nucleophile and the substrate, making it second-order. Steric hindrance significantly affects the rate, with primary substrates reacting faster than secondary or tertiary ones.

E2 Reactions

E2 (Elimination Bimolecular) reactions are characterized by the simultaneous removal of a leaving group and a hydrogen atom from adjacent carbon atoms, leading to the formation of a double bond. This reaction also occurs in a single step and is second-order, depending on the concentrations of both the substrate and the base. The reaction rate is influenced by the strength of the base and the structure of the substrate, with bulky bases favoring more sterically accessible sites.

Reaction Conditions

The rate of SN2 and E2 reactions can be influenced by various factors, including solvent type, temperature, and substrate structure. Polar aprotic solvents favor SN2 reactions by stabilizing the nucleophile without solvation, while strong bases and high temperatures enhance E2 reactions. Understanding these conditions is crucial for predicting which reaction will proceed faster under specific circumstances.

Watch next

Master Overview of the flowchart. with a bite sized video explanation from Johnny

Start learning