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 - Anti-Coplanar Requirement

Organic Chemistry

8. Elimination Reactions

E2 - Anti-Coplanar Requirement

Previous problemNext problem

Problem 45

Textbook Question

The cis-diastereomer undergoes E2 elimination 500 times faster than the trans form. Explain.

Verified step by step guidance

Understand the E2 elimination mechanism: E2 elimination is a bimolecular reaction where a base removes a proton (β-hydrogen) from the β-carbon, and simultaneously, the leaving group departs from the α-carbon, forming a double bond. The reaction requires a specific geometric arrangement called anti-periplanar geometry.

Recognize the importance of anti-periplanar geometry: In E2 elimination, the β-hydrogen and the leaving group must be positioned opposite to each other in the same plane (anti-periplanar) for the reaction to proceed efficiently. This geometry allows for optimal orbital overlap during the elimination process.

Analyze the cis-diastereomer: In the cis-diastereomer, the β-hydrogen and the leaving group are more likely to adopt the anti-periplanar geometry due to the spatial arrangement of substituents. This makes the elimination process faster because the required geometry is readily achieved.

Analyze the trans-diastereomer: In the trans-diastereomer, the β-hydrogen and the leaving group are less likely to adopt the anti-periplanar geometry due to steric hindrance or unfavorable spatial arrangement. This reduces the efficiency of the elimination process, making it slower compared to the cis-diastereomer.

Conclude the explanation: The cis-diastereomer undergoes E2 elimination 500 times faster than the trans form because the anti-periplanar geometry is more easily achieved in the cis-diastereomer, facilitating the elimination reaction. The trans-diastereomer faces geometric constraints that hinder the reaction.

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.

Cis-Trans Isomerism

Cis-trans isomerism, also known as geometric isomerism, occurs in compounds with restricted rotation around a double bond or a ring structure. In this context, 'cis' refers to isomers where substituents are on the same side of the double bond, while 'trans' indicates they are on opposite sides. This spatial arrangement significantly influences the physical and chemical properties of the molecules, including their reactivity.

E2 Elimination Mechanism

The E2 elimination mechanism is a type of bimolecular elimination reaction where a base removes a proton from a β-carbon, leading to the formation of a double bond and the expulsion of a leaving group. This mechanism is concerted, meaning that bond-breaking and bond-forming occur simultaneously. The stereochemistry of the substrate plays a crucial role in determining the reaction rate, with certain conformations favoring faster elimination.

Steric Hindrance and Transition States

Steric hindrance refers to the repulsion between bulky groups in a molecule that can impede reactions. In the context of E2 eliminations, the transition state is influenced by the spatial arrangement of substituents. The cis-diastereomer may have a more favorable transition state due to less steric hindrance compared to the trans form, allowing for a faster reaction rate in the elimination process.

Watch next

Master The Anti-Coplanar Requirement with a bite sized video explanation from Johnny

Start learning

Related Videos

Related Practice

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

a. Design an alkyl halide that will give only 2,4-diphenylpent-2-ene upon treatment with potassium tert-butoxide (a bulky base that promotes E2 elimination).

b. What stereochemistry is required in your alkyl halide so that only the following stereoisomer of the product is formed?

Textbook Question

One of the following dichloronorbornanes undergoes elimination much faster than the other. Determine which one reacts faster, and explain the large difference in rates.

Textbook Question

Give the expected product(s) of E2 elimination for each reaction. (Hint: Use models!)

(a)

Textbook Question

Which reactant in each of the following pairs undergoes an elimination reaction more rapidly? Explain your choice.

Textbook Question

Explain why only a substitution product and no elimination product is obtained when the following compound reacts with sodium methoxide:

Textbook Question

For each of the following compounds, draw the product that forms in an E2 reaction and indicate its configuration:

b. (1S,2R)-1-bromo-1,2-diphenylpropane

Textbook Question

Why do cis-1-bromo-2-ethylcyclohexane and trans-1-bromo-2-ethylcyclohexane form different major products when they undergo an E2 reaction?

Show more practices

Download the Mobile app

Privacy

Do not sell my personal information

Accessibility

Patent notice

Sitemap