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

3. Acids and Bases

Reaction Mechanism

Organic Chemistry

3. Acids and Bases

Reaction Mechanism

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Problem 17b

Textbook Question

Provide an arrow-pushing mechanism for the following hypothetical base half-reactions.
(b)

Verified step by step guidance

Step 1: Identify the nucleophile and electrophile in the reaction. The oxygen atom with lone pairs in the ketone acts as the nucleophile, while the H⁺ (proton) acts as the electrophile.

Step 2: Draw the curved arrow to represent the movement of electrons. The lone pair of electrons on the oxygen atom will attack the H⁺, forming a bond between the oxygen and hydrogen.

Step 3: Update the structure of the ketone after the protonation. The oxygen atom now has a positive charge due to the addition of the proton, as it has gained a bond but lost one lone pair.

Step 4: Ensure the reaction is balanced. Verify that the number of atoms and charges are conserved in the reaction. The protonation of the ketone does not alter the carbon skeleton.

Step 5: Review the mechanism for clarity. Confirm that the arrow-pushing correctly represents the electron flow from the nucleophile (oxygen) to the electrophile (H⁺), resulting in the protonated ketone.

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Key Concepts

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

Arrow-Pushing Mechanism

Arrow-pushing is a notation used in organic chemistry to illustrate the movement of electrons during chemical reactions. It involves using arrows to show the direction of electron flow, indicating how bonds are formed or broken. This mechanism is crucial for visualizing reaction pathways, especially in acid-base reactions where proton transfer occurs.

Acid-Base Reactions

Acid-base reactions involve the transfer of protons (H+) between reactants. An acid donates a proton, while a base accepts it. Understanding the strength of acids and bases, as well as their conjugate pairs, is essential for predicting the outcome of these reactions and for applying the arrow-pushing mechanism correctly.

Conjugate Acid-Base Pairs

Conjugate acid-base pairs consist of two species that differ by the presence or absence of a proton. When an acid donates a proton, it becomes its conjugate base, and when a base accepts a proton, it becomes its conjugate acid. Recognizing these pairs is vital for understanding the equilibrium of acid-base reactions and the stability of the resulting species.

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Related Practice

Textbook Question

In each case, circle the stronger nucleophile.

(d)

Textbook Question

We show in Chapter 20 that α , β-unsaturated ketones are electrophilic at C₄. Rationalize this observation.

Textbook Question

In each case, circle the stronger nucleophile.

(c)

Textbook Question

Provide a reasonable arrow-pushing mechanism for the following Lewis acid–Lewis base reactions.

(a)

Textbook Question

BCl₃ has an empty p orbital, so it is a strong Lewis acid. Would you expect an amide to react with BCl₃ at nitrogen or oxygen?

Textbook Question

In each case, circle the stronger nucleophile.

(b)

Textbook Question

Based on the analysis you used in Assessment 17.3, which carbonyl would you expect to react most quickly with a nucleophile?

(c)

Textbook Question

Classify the following nucleophiles as strong, weak, or intermediate. Would you expect each to add to a carbonyl directly or wait for a carbocation to form?

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Provide an arrow-pushing mechanism for the following hypothetical base half-reactions.(b)

Key Concepts

Arrow-Pushing Mechanism

Acid-Base Reactions

Conjugate Acid-Base Pairs

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Provide an arrow-pushing mechanism for the following hypothetical base half-reactions.
(b)