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

4. Alkanes and Cycloalkanes

Cis vs Trans

Organic Chemistry

4. Alkanes and Cycloalkanes

Cis vs Trans

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6:04 minutes

Problem 10

Textbook Question

Why does cis-2-butene have a higher boiling point than trans-2-butene?

Verified step by step guidance

Understand the structural difference between cis-2-butene and trans-2-butene. Cis-2-butene has both methyl groups on the same side of the double bond, while trans-2-butene has the methyl groups on opposite sides of the double bond.

Recognize that the spatial arrangement of the methyl groups in cis-2-butene creates a dipole moment. The molecule is slightly polar because the electron density is unevenly distributed due to the methyl groups being on the same side.

Compare this to trans-2-butene, which is nonpolar. In trans-2-butene, the methyl groups are on opposite sides, canceling out any dipole moment and resulting in a more symmetrical molecule.

Understand that intermolecular forces play a key role in boiling points. Cis-2-butene, being slightly polar, experiences stronger dipole-dipole interactions compared to trans-2-butene, which only experiences weaker London dispersion forces.

Conclude that the stronger intermolecular forces in cis-2-butene require more energy to overcome during boiling, leading to a higher boiling point compared to trans-2-butene.

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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. In cis isomers, substituents are on the same side of the double bond, while in trans isomers, they are on opposite sides. This spatial arrangement affects the physical properties of the molecules, including boiling points.

Polarity and Intermolecular Forces

The boiling point of a substance is influenced by its intermolecular forces, which include hydrogen bonding, dipole-dipole interactions, and London dispersion forces. Cis-2-butene is more polar than trans-2-butene due to its molecular geometry, leading to stronger dipole-dipole interactions. This increased polarity results in a higher boiling point for cis-2-butene.

Boiling Point Trends

Boiling point trends in organic compounds are often determined by molecular weight, structure, and intermolecular forces. Generally, compounds with stronger intermolecular forces have higher boiling points. In the case of cis-2-butene versus trans-2-butene, the stronger dipole-dipole interactions in the cis form contribute to its higher boiling point compared to the trans form.

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