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

E2 Mechanism

Organic Chemistry

8. Elimination Reactions

E2 Mechanism

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2:34 minutes

Problem 83e

Textbook Question

Draw the major product obtained when each of the following alkyl halides undergoes an E2 reaction:
e.

Verified step by step guidance

Identify the alkyl halide structure and classify it as primary, secondary, or tertiary. This classification will help determine the reactivity and the likelihood of elimination (E2) over substitution (SN2).

Recall the E2 mechanism: it is a one-step, concerted reaction where a strong base abstracts a β-hydrogen (hydrogen on a carbon adjacent to the carbon bearing the leaving group), and the leaving group departs simultaneously, forming a double bond.

Locate all β-hydrogens in the molecule. Identify the β-carbon(s) adjacent to the carbon bonded to the leaving group. These β-hydrogens are potential candidates for elimination.

Determine the most substituted alkene product (Zaitsev's rule) as the major product. The base will preferentially abstract a β-hydrogen that leads to the formation of the more stable, highly substituted alkene. However, if a bulky base is used, the less substituted alkene (Hofmann product) may dominate.

Draw the structure of the major alkene product, ensuring proper placement of the double bond between the α-carbon (carbon bearing the leaving group) and the β-carbon from which the hydrogen was removed.

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Key Concepts

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

E2 Reaction Mechanism

The E2 (bimolecular elimination) reaction is a type of elimination reaction where a base removes a proton from a β-carbon while a leaving group departs from the α-carbon simultaneously. This concerted mechanism results in the formation of a double bond between the α and β carbons. Understanding the stereochemistry and the requirement for anti-periplanar geometry is crucial for predicting the major product.

Alkyl Halides

Alkyl halides are organic compounds containing a carbon atom bonded to a halogen atom (F, Cl, Br, I). They serve as substrates in various reactions, including E2 eliminations. The structure of the alkyl halide, such as whether it is primary, secondary, or tertiary, significantly influences the reaction pathway and the stability of the resulting alkene.

Base Strength and Sterics

The strength and steric properties of the base used in an E2 reaction are critical for determining the reaction's outcome. Strong bases, such as alkoxides or hydrides, favor E2 mechanisms, while bulky bases can lead to different regioselectivity. Additionally, the steric hindrance around the alkyl halide can affect the accessibility of the β-hydrogen, influencing the formation of the major product.

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Related Practice

Textbook Question

cis-4-Bromocyclohexanol and trans-4-bromocyclohexanol form the same elimination product but a different substitution product when they react with HO⁻.

a. Why do they form the same elimination product?

Textbook Question

a. Explain why 1-bromo-2,2-dimethylpropane has difficulty undergoing both S_N2 and S_N1 reactions.

b. Can it undergo E2 and E1 reactions?

Textbook Question

What is the major elimination product obtained from an E2 reaction of each of the following alkyl halides with hydroxide ion?

Textbook Question

What products will be obtained from the E2 reaction of the following alkyl halides?

Textbook Question

When 2-bromopropane is treated with sodium ethoxide, propene is produced. What molecule is lost from 2-bromopropane in this process?

Textbook Question

Justify on a reaction coordinate diagram the fact that a strong base like sodium amide (NaNH₂) results in a faster E2 elimination than does sodium hydroxide (NaOH).

Textbook Question

Practice your electron-pushing skills by drawing a mechanism for the following E2 reactions.

(a)

Textbook Question

Suggest a mechanism for the following elimination reactions.

(c)

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