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

Previous problemNext problem

4:46 minutes

Problem 69c,d

Textbook Question

Which member in each pair in [PROBLEM 9-68] is a better leaving group?
c. H₂O or H₂S
d. HO⁻ or HS⁻

Verified step by step guidance

Step 1: Understand the concept of a leaving group. A leaving group is an atom or group of atoms that can depart with a pair of electrons during a chemical reaction, such as a substitution or elimination reaction. A good leaving group is typically weakly basic and stable after leaving.

Step 2: Compare the acidity of the conjugate acids of the leaving groups. The strength of a leaving group is inversely related to the basicity of the group. The weaker the base, the better the leaving group. For example, the conjugate acids of H2O and H2S are H3O+ and H3S+, respectively. Similarly, the conjugate acids of HO− and HS− are H2O and H2S, respectively.

Step 3: Analyze the stability of the leaving group after departure. Stability is influenced by factors such as electronegativity, size, and polarizability. Larger and more polarizable atoms (like sulfur) tend to stabilize the negative charge better than smaller atoms (like oxygen).

Step 4: For part (c), compare H2O and H2S. H2S is a weaker base than H2O because sulfur is less electronegative and more polarizable than oxygen. Therefore, H2S is a better leaving group than H2O.

Step 5: For part (d), compare HO− and HS−. HS− is a weaker base than HO− for the same reasons as above (sulfur is less electronegative and more polarizable than oxygen). Thus, HS− is a better leaving group than HO−.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

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, typically in nucleophilic substitution or elimination reactions. A good leaving group is stable after departure, often being a weak base. The ability of a leaving group to stabilize its negative charge or form a stable molecule is crucial in determining its effectiveness.

Acid-Base Strength

The strength of an acid or base is a key factor in determining the quality of a leaving group. Stronger acids have weaker conjugate bases, which tend to be better leaving groups. For example, H2O is the conjugate base of a strong acid (H3O+), making it a better leaving group than H2S, which is the conjugate base of a weaker acid (H2S).

Nucleophilicity vs. Leaving Group Ability

Nucleophilicity refers to the ability of a species to donate an electron pair to form a bond, while leaving group ability is about how well a species can depart from a molecule. Generally, a good nucleophile is a poor leaving group and vice versa. Understanding this relationship helps in predicting reaction pathways and the stability of intermediates.

Watch next

Master How to use the factors affecting acidity to predict leaving group ability. with a bite sized video explanation from Johnny

Start learning