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

7. Substitution Reactions

Good Leaving Groups

Organic Chemistry

7. Substitution Reactions

Good Leaving Groups

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1:59 minutes

Problem 25a

Textbook Question

Which of the following is the better leaving group in a polar aprotic solvent?
(a) HO⁻ vs. F⁻

Verified step by step guidance

Understand the concept of leaving groups: A leaving group is an atom or group of atoms that can depart with a pair of electrons during a chemical reaction. A better leaving group is typically more stable after leaving, often due to its ability to stabilize the negative charge.

Recall the effect of the solvent: In a polar aprotic solvent, the solvent does not donate hydrogen bonds to stabilize ions. This means that the leaving group's stability depends more on its intrinsic properties rather than solvent interactions.

Compare the basicity of the leaving groups: Basicity is inversely related to leaving group ability. A weaker base is a better leaving group because it is more stable after leaving. Hydroxide ion (HO⁻) is a stronger base than fluoride ion (F⁻), as oxygen is less electronegative than fluorine.

Consider the electronegativity of the atoms: Fluorine is more electronegative than oxygen, meaning it can better stabilize the negative charge when it becomes F⁻. This makes F⁻ a better leaving group than HO⁻ in general.

Conclude based on the solvent and properties: In a polar aprotic solvent, F⁻ is the better leaving group compared to HO⁻ because it is less basic and more stable as an ion due to its high electronegativity.

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Key Concepts

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

Leaving Groups

Leaving groups are atoms or groups of atoms that can depart from a molecule during a chemical reaction, taking with them the electrons that were shared with the molecule. A good leaving group is typically stable after departure, which allows for smoother reaction pathways. Common examples include halides and water, while poor leaving groups include hydroxide (OH⁻) and fluoride (F⁻).

Polar Aprotic Solvents

Polar aprotic solvents are solvents that have a significant dipole moment but do not have hydrogen atoms bonded to electronegative atoms, which means they cannot form hydrogen bonds. These solvents can stabilize cations and polarize anions, enhancing the reactivity of nucleophiles. Examples include acetone and dimethyl sulfoxide (DMSO), which are often used in reactions involving strong nucleophiles.

Nucleophilicity and Basicity

Nucleophilicity refers to the ability of a species to donate an electron pair to an electrophile, while basicity measures the tendency of a species to accept protons. In polar aprotic solvents, nucleophilicity is often enhanced for anions because these solvents do not solvate anions as effectively as protic solvents. This distinction is crucial when comparing the leaving groups HO⁻ and F⁻, as their stability and reactivity can vary significantly in different solvent environments.

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