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

SN2 Reaction

Organic Chemistry

7. Substitution Reactions

SN2 Reaction

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4:13 minutes

Problem 9a,b

Textbook Question

Which alkyl halide is more reactive in an S_N2 reaction with a given nucleophile?
a.
b.

Verified step by step guidance

Step 1: Understand the SN2 reaction mechanism. SN2 reactions are bimolecular nucleophilic substitution reactions where the nucleophile attacks the electrophilic carbon and displaces the leaving group in a single step. The rate of the reaction depends on steric hindrance and the quality of the leaving group.

Step 2: Analyze the structures in part (a). The first structure has a primary alkyl bromide, while the second structure has a secondary alkyl bromide. Primary alkyl halides are less sterically hindered compared to secondary alkyl halides, making them more reactive in SN2 reactions.

Step 3: Analyze the structures in part (b). The first structure has a chlorine atom as the leaving group, while the second structure has an iodine atom. Iodine is a better leaving group than chlorine because it is larger and more polarizable, which stabilizes the negative charge after leaving.

Step 4: Compare the reactivity of the alkyl halides in part (a). The primary alkyl bromide is more reactive in an SN2 reaction than the secondary alkyl bromide due to reduced steric hindrance.

Step 5: Compare the reactivity of the alkyl halides in part (b). The alkyl iodide is more reactive in an SN2 reaction than the alkyl chloride because iodine is a superior leaving group compared to chlorine.

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Key Concepts

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

SN2 Mechanism

The SN2 (substitution nucleophilic bimolecular) mechanism involves a single concerted step where a nucleophile attacks an electrophile, leading to the simultaneous displacement of a leaving group. This reaction is characterized by a backside attack, which results in inversion of configuration at the carbon center. The rate of the reaction depends on both the nucleophile and the substrate, making it bimolecular.

Leaving Group Ability

The ability of a leaving group to depart from a substrate is crucial in determining the reactivity of alkyl halides in SN2 reactions. Good leaving groups, such as bromide (Br-) and iodide (I-), stabilize the negative charge after leaving, facilitating the reaction. In contrast, poor leaving groups, like chloride (Cl-), hinder the reaction, making the substrate less reactive.

Steric Hindrance

Steric hindrance refers to the spatial arrangement of atoms around a reactive center that can impede the approach of a nucleophile. In SN2 reactions, primary alkyl halides are more reactive than secondary or tertiary ones due to less steric hindrance. The presence of bulky groups around the electrophilic carbon can significantly slow down or prevent the nucleophilic attack.

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Related Practice

Textbook Question

Draw the substitution product formed by each of the following S_N2 reactions:

a. trans-1-iodo-4-ethylcyclohexane and methoxide ion

b. cis-1-chloro-3-methylcyclobutane and ethoxide ion

Textbook Question

Draw the products obtained from the S_N2 reaction of:

c. (S)-3-chlorohexane and hydroxide ion.

d. 3-iodopentane and hydroxide ion.

Textbook Question

Which alkyl halide is more reactive in an S_N2 reaction with a given nucleophile?

Textbook Question

Rank the following alkyl bromides from most reactive to least reactive in an S_N2 reaction:

1-bromo-2-methylbutane, 1-bromo-3-methylbutane, 2-bromo-2-methylbutane, and 1-bromopentane.

Textbook Question

Does increasing the energy barrier for an S_N2 reaction increase or decrease the magnitude of the rate constant for the reaction?

Textbook Question

The rate of the reaction of methyl iodide with quinuclidine was measured in nitrobenzene, and then the rate of the reaction of methyl iodide with triethylamine was measured in the same solvent. The concentration of the reagents was the same in both experiments.

a.Which reaction had the larger rate constant?

Textbook Question

Draw a transition state for the following substitution reaction.

Textbook Question

Predict the major products of the following reactions.

(a) ethyl tosylate + potassium tert-butoxide

(b) isobutyl tosylate + NaI

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