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)

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6:26 minutes

Problem 27b

Textbook Question

Make models of the following compounds, and predict the products formed when they react with the strong bases shown.
(b) meso-1,2-dibromo-1,2-diphenylethane + (CH₃CH₂)₃N:

Verified step by step guidance

Step 1: Analyze the structure of meso-1,2-dibromo-1,2-diphenylethane. This compound is a meso compound, meaning it has a plane of symmetry and is achiral despite having stereocenters. The two bromine atoms are on adjacent carbons, and the phenyl groups are attached to the same carbons as the bromine atoms.

Step 2: Recall the mechanism of an E2 elimination reaction. E2 eliminations require a strong base and a β-hydrogen that is anti-periplanar (in the opposite plane) to the leaving group (in this case, bromine). The base abstracts the β-hydrogen, and the leaving group departs simultaneously, forming a double bond.

Step 3: Identify the β-hydrogens in meso-1,2-dibromo-1,2-diphenylethane. The β-hydrogens are on the carbons adjacent to the carbons bearing the bromine atoms. Since the compound is meso, the β-hydrogens are positioned anti-periplanar to the bromine atoms, making them suitable for E2 elimination.

Step 4: Predict the product of the E2 elimination. When the strong base (triethylamine, (CH3CH2)3N:) abstracts a β-hydrogen, the electrons from the C-H bond form a π-bond between the two carbons, and the bromine atom leaves as a bromide ion. This results in the formation of a double bond between the two carbons, yielding a trans-stilbene product (E-1,2-diphenylethene).

Step 5: Consider the stereochemistry of the product. Since the elimination occurs via an anti-periplanar mechanism, the resulting product will have the trans (E) configuration, as this is the most stable arrangement of the phenyl groups due to minimized steric hindrance.

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Key Concepts

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

E2 Elimination Mechanism

The E2 elimination mechanism is a bimolecular reaction where a strong base abstracts a proton from a β-carbon while a leaving group departs from the adjacent α-carbon, resulting in the formation of a double bond. This process typically requires the hydrogen and leaving group to be anti-coplanar, meaning they are on opposite sides of the molecule, which facilitates the elimination and stabilizes the transition state.

Anti-Coplanar vs. Syn-Coplanar

In the context of E2 eliminations, anti-coplanar refers to the spatial arrangement where the leaving group and the hydrogen being removed are positioned 180 degrees apart, which is ideal for the reaction. Conversely, syn-coplanar arrangements, where these groups are on the same side, are less favorable and occur only under specific conditions, such as when rotation around a bond is restricted.

Meso Compounds

Meso compounds are achiral molecules that contain multiple stereocenters but possess an internal plane of symmetry. In the case of meso-1,2-dibromo-1,2-diphenylethane, the presence of this symmetry means that despite having stereocenters, the compound does not exhibit optical activity, which can influence the products formed during elimination reactions.

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Make models of the following compounds, and predict the products formed when they react with the strong bases shown.(b) meso-1,2-dibromo-1,2-diphenylethane + (CH3CH2)3N:

Key Concepts

E2 Elimination Mechanism

Anti-Coplanar vs. Syn-Coplanar

Meso Compounds

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Make models of the following compounds, and predict the products formed when they react with the strong bases shown.
(b) meso-1,2-dibromo-1,2-diphenylethane + (CH₃CH₂)₃N: