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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Problem 91

Textbook Question

A trifluoromethanesulfonate (triflate) can be used in a manner similar to tosylates. Which would you expect to be a better leaving group? Why?

Verified step by step guidance

Step 1: Understand the concept of leaving groups. A good leaving group is one that can stabilize the negative charge after it departs from the molecule. This stability is often influenced by resonance, electronegativity, and inductive effects.

Step 2: Analyze the structure of tosylate. The tosylate group contains a benzene ring attached to a sulfonate group. The benzene ring provides resonance stabilization for the negative charge on the oxygen atoms of the sulfonate group, making it a relatively good leaving group.

Step 3: Analyze the structure of triflate. The triflate group contains a trifluoromethyl group attached to a sulfonate group. The trifluoromethyl group is highly electronegative due to the presence of three fluorine atoms, which exert a strong inductive effect. This inductive effect pulls electron density away from the sulfonate group, further stabilizing the negative charge on the oxygen atoms.

Step 4: Compare the stabilization mechanisms. While both tosylate and triflate stabilize the negative charge, triflate benefits from both inductive effects (from the electronegative fluorine atoms) and resonance stabilization within the sulfonate group. The trifluoromethyl group enhances the stability of the leaving group more effectively than the benzene ring in tosylate.

Step 5: Conclude that triflate is expected to be a better leaving group than tosylate due to the stronger inductive effect provided by the trifluoromethyl group, which leads to greater stabilization of the negative charge after departure.

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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 involved in the bond. A good leaving group is typically stable after departure and can stabilize the negative charge, making it more favorable for the reaction to proceed. Common examples include halides and sulfonate groups.

Trifluoromethanesulfonate (Triflate)

Trifluoromethanesulfonate, or triflate, is a sulfonate ester derived from trifluoromethanesulfonic acid. It is known for being an excellent leaving group due to the strong electron-withdrawing effect of the three fluorine atoms, which stabilize the negative charge on the leaving group after it departs. This property makes triflates highly reactive in nucleophilic substitution reactions.

Tosylates

Tosylates are derivatives of tosyl acid and serve as good leaving groups in organic reactions. The tosyl group (–OTs) is stable and can effectively stabilize the negative charge upon leaving. While tosylates are good leaving groups, triflates are generally considered superior due to their enhanced stability and reactivity, primarily attributed to the electronegative fluorine atoms in triflates.

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