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 - Cumulative Practice

Organic Chemistry

8. Elimination Reactions

E2 - Cumulative Practice

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7:12 minutes

Problem 111a,b

Textbook Question

Draw the elimination products for each of the following E2 reactions; if the products can exist as stereoisomers, indicate which stereoisomers are obtained.
a. (2S,3S)-2-chloro-3-methylpentane + high concentration of CH₃O⁻
b. (2S,3R)-2-chloro-3-methylpentane + high concentration of CH₃O⁻

Verified step by step guidance

Step 1: Understand the E2 elimination mechanism. E2 (bimolecular elimination) is a one-step reaction where a base abstracts a proton (β-hydrogen) from the β-carbon, and the leaving group (e.g., Cl⁻) departs simultaneously, forming a double bond. The reaction requires an anti-periplanar geometry between the β-hydrogen and the leaving group.

Step 2: Analyze the structure of (2S, 3S)-2-chloro-3-methylpentane. Draw the molecule in its correct stereochemical configuration. Identify the β-hydrogens on the β-carbons adjacent to the carbon bearing the leaving group (Cl). Ensure you consider the anti-periplanar geometry for elimination.

Step 3: Determine the possible elimination products for (2S, 3S)-2-chloro-3-methylpentane. The double bond will form between the α-carbon (carbon bearing the leaving group) and the β-carbon. Check if the products can exist as stereoisomers (E/Z isomers) based on the substituents around the double bond.

Step 4: Repeat the process for (2S, 3R)-2-chloro-3-methylpentane. Draw the molecule in its correct stereochemical configuration. Identify the β-hydrogens and ensure the anti-periplanar geometry is satisfied for elimination. Predict the possible elimination products and check for stereoisomers.

Step 5: Summarize the elimination products for both (2S, 3S)-2-chloro-3-methylpentane and (2S, 3R)-2-chloro-3-methylpentane. Indicate the stereoisomers (E/Z) obtained for each case, if applicable. Note that the stereochemistry of the starting material influences the stereochemistry of the products due to the anti-periplanar requirement.

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Key Concepts

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

E2 Mechanism

The E2 mechanism is a type of elimination reaction where a base removes a proton from a β-carbon, leading to the simultaneous departure of a leaving group from the α-carbon. This concerted process results in the formation of a double bond. Understanding the stereochemistry of the starting material is crucial, as it influences the stereochemical outcome of the elimination products.

Stereoisomerism

Stereoisomerism refers to the phenomenon where compounds have the same molecular formula and connectivity but differ in the spatial arrangement of atoms. In E2 reactions, the stereochemistry of the starting material can lead to different stereoisomers in the products, such as cis and trans configurations, or E/Z isomers, depending on the orientation of substituents around the double bond formed.

Regioselectivity and Stereoselectivity

Regioselectivity and stereoselectivity are important concepts in elimination reactions. Regioselectivity refers to the preference for the formation of one constitutional isomer over others, while stereoselectivity indicates the preference for one stereoisomer over another. In E2 reactions, the orientation of the leaving group and the hydrogen being removed can lead to different regio- and stereoisomeric products, which must be considered when predicting the outcomes.

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