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

9. Alkenes and Alkynes

Dehydration Reaction

Organic Chemistry

9. Alkenes and Alkynes

Dehydration Reaction

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Problem 73c

Textbook Question

Suggest a mechanism for the following reactions.
(c) Elimination:

Verified step by step guidance

Step 1: Protonation of the alcohol group - The reaction begins with the alcohol group (-OH) being protonated by sulfuric acid (H₂SO₄). This converts the hydroxyl group into a better leaving group, forming water (H₂O). The protonation step can be represented as:

{R OH}_{+} H {SO}_{4} \to {R OH}_{H}

Step 2: Formation of the carbocation - After protonation, the water molecule leaves, generating a carbocation intermediate. This step is crucial as it determines the stability of the intermediate. The carbocation formed is tertiary, which is highly stable due to hyperconjugation and inductive effects.

Step 3: Rearrangement (if necessary) - In some cases, carbocation rearrangement may occur to form a more stable carbocation. However, in this reaction, the carbocation is already tertiary and stable, so no rearrangement is needed.

Step 4: Elimination of a proton - A base (often the bisulfate ion, HSO₄⁻, from sulfuric acid) abstracts a proton from a β-carbon adjacent to the carbocation. This leads to the formation of a double bond (alkene) via the E1 elimination mechanism. The most substituted alkene is formed due to Zaitsev's rule.

Step 5: Final product formation - The reaction concludes with the formation of the alkene product (2-methylcyclohexene) and water as a byproduct. The alkene is the major product due to its stability and adherence to Zaitsev's rule.

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Key Concepts

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

Elimination Reactions

Elimination reactions involve the removal of atoms or groups from a molecule, resulting in the formation of a double bond or a ring structure. In organic chemistry, these reactions often occur with the loss of a small molecule, such as water or hydrogen halide. The most common types are E1 and E2 mechanisms, which differ in their steps and conditions.

Acid-Catalyzed Dehydration

Acid-catalyzed dehydration is a specific type of elimination reaction where an alcohol is converted into an alkene through the removal of water. In this process, an acid, such as sulfuric acid (H2SO4), protonates the alcohol, making it a better leaving group. This leads to the formation of a carbocation intermediate, which can then lose a proton to form the double bond.

Carbocation Stability

Carbocation stability is crucial in elimination reactions, as the stability of the carbocation intermediate influences the reaction pathway. Carbocations are classified as primary, secondary, or tertiary based on the number of alkyl groups attached to the positively charged carbon. Tertiary carbocations are the most stable due to hyperconjugation and inductive effects, making them more favorable in elimination mechanisms.

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Related Practice

Textbook Question

Identify the alcohol(s) that would produce the following alkenes under the given conditions.

(b)

Textbook Question

Identify the alcohol(s) that would produce the following alkenes under the given conditions.

(c)

Textbook Question

When using sulfuric acid, but in the absence of other nucleophiles like water or bromide ion, less stable alkenes can be isomerized to their more stable isomer. Provide a mechanism for these acid-catalyzed isomerization reactions. [This is one illustration of the principle of microscopic reversibility.]

(a)

Textbook Question

Predict the product of the following pinacol rearrangements.

(c)

Textbook Question

Suggest a mechanism for the following substitution reaction.

Textbook Question

Predict the product(s) that would result when molecules (a)–(p) are allowed to react under the following conditions: (vi) H₂SO₄. If no reaction occurs, write 'no reaction.'

(a)

Textbook Question

The acid-catalyzed hydration we learned here in Chapter 8 is reversible:

Textbook Question

What product is obtained when the following vicinal diol is heated in an acidic solution?

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