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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6:19 minutes

Problem 69e,f

Textbook Question

Which member in each pair in [PROBLEM 9-68] is a better leaving group?
e. I⁻ or Br⁻
f. Cl⁻ or Br⁻

Verified step by step guidance

Step 1: Understand the concept of leaving groups. A leaving group is an atom or group that detaches from the parent molecule during a chemical reaction, typically in substitution or elimination reactions. The better leaving group is usually the one that can stabilize the negative charge after leaving.

Step 2: Recall the periodic trends in electronegativity and size. Larger atoms tend to stabilize negative charges better due to their ability to spread out the charge over a larger volume. This is important for determining the relative ability of halide ions (I−, Br−, Cl−) to act as leaving groups.

Step 3: Compare the size of the halide ions. Iodide (I−) is larger than bromide (Br−), and bromide (Br−) is larger than chloride (Cl−). The larger the ion, the better it can stabilize the negative charge, making it a better leaving group.

Step 4: Consider the bond strength between the halide and the carbon atom in the molecule. A weaker bond is easier to break, which also contributes to the halide's ability to act as a leaving group. I− forms weaker bonds compared to Br−, and Br− forms weaker bonds compared to Cl−.

Step 5: Based on these factors, evaluate each pair: (e) I− vs. Br− and (f) Cl− vs. Br−. The larger halide ion in each pair will generally be the better leaving group due to its ability to stabilize the negative charge more effectively.

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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, typically in nucleophilic substitution or elimination reactions. A good leaving group is one that can stabilize the negative charge after departure, often due to its ability to resonate or its size. Common examples include halides like I−, Br−, and Cl−, with their effectiveness generally increasing down the group in the periodic table.

Nucleophilicity and Electronegativity

Nucleophilicity refers to the ability of a species to donate an electron pair to an electrophile, while electronegativity is a measure of an atom's ability to attract electrons. In the context of leaving groups, more electronegative atoms tend to hold onto their electrons more tightly, making them poorer leaving groups. Conversely, larger atoms like iodine are less electronegative and can stabilize the negative charge better, making them better leaving groups.

Stability of Leaving Groups

The stability of a leaving group after it departs is crucial in determining its effectiveness. A stable leaving group can better accommodate the negative charge, which is often the case for larger halides. For instance, I− is more stable than Br− or Cl− due to its larger size and lower electronegativity, making it a better leaving group in reactions compared to the other halides.

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