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

6. Thermodynamics and Kinetics

Energy Diagram

Organic Chemistry

6. Thermodynamics and Kinetics

Energy Diagram

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3:40 minutes

Problem 38

Textbook Question

a. Draw an approximate reaction-energy diagram for the acid–base reaction of phenol (see below) with 1-molar aqueous sodium hydroxide solution.
b. On the same diagram, draw an approximate reaction-energy diagram for the acid–base reaction of tert-butyl alcohol (see below) with 1-molar aqueous sodium hydroxide solution.

Verified step by step guidance

Analyze the given chemical structures and pKa values: Phenol has a pKa of 10.0, indicating it is more acidic than tert-butyl alcohol, which has a pKa of 18.0. Lower pKa values correspond to stronger acids.

Understand the acid-base reaction: In both cases, the hydroxide ion (OH⁻) from the sodium hydroxide solution will act as a base and deprotonate the alcohol group (-OH) of phenol and tert-butyl alcohol, forming their conjugate bases (phenoxide ion and tert-butoxide ion, respectively).

Sketch the reaction-energy diagram for phenol: The diagram should show the reactants (phenol and OH⁻) at a higher energy level than the products (phenoxide ion and water). The energy barrier (activation energy) for the reaction will be relatively low due to phenol's higher acidity.

Sketch the reaction-energy diagram for tert-butyl alcohol: The reactants (tert-butyl alcohol and OH⁻) will be at a higher energy level than the products (tert-butoxide ion and water). However, the energy barrier for this reaction will be higher compared to phenol due to tert-butyl alcohol's lower acidity.

Compare the diagrams: On the same graph, the reaction-energy diagram for phenol will show a lower activation energy and a greater energy difference between reactants and products compared to tert-butyl alcohol, reflecting the stronger acidity of phenol.

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Key Concepts

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

Acid-Base Reactions

Acid-base reactions involve the transfer of protons (H+) between reactants. In this context, phenol and tert-butyl alcohol act as acids, donating protons to the hydroxide ion (OH-) from sodium hydroxide. The strength of an acid is often measured by its pKa value, which indicates the tendency of the acid to lose a proton; lower pKa values correspond to stronger acids.

pKa Values

The pKa value is a quantitative measure of the strength of an acid in solution. It is the negative logarithm of the acid dissociation constant (Ka). For phenol, with a pKa of 10.0, it is a relatively stronger acid compared to tert-butyl alcohol, which has a pKa of 18.0, indicating that phenol will more readily donate a proton in an acid-base reaction.

Reaction Energy Diagrams

A reaction energy diagram visually represents the energy changes during a chemical reaction. It typically shows the energy of reactants, products, and the transition state. In the context of acid-base reactions, the diagram will illustrate the energy required to break bonds and form new ones, highlighting the stability of the reactants and products based on their pKa values.

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Related Practice

Textbook Question

Draw the reaction-energy diagram for the following reverse reaction:

•CH₃ + HCl → CH₄ + Cl•

Textbook Question

Draw a reaction-energy diagram for the following reaction:

•CH₃ + Cl₂ → CH₃Cl + Cl•

The activation energy is 4 kJ/mol (1 kcal/mol), and the overall ΔH° for the reaction is –110 kJ/mol (–27 kcal/mol).

Textbook Question

•CH₃ + Cl₂ → CH₃Cl + Cl•

The activation energy is 4 kJ/mol (1 kcal/mol), and the overall ΔH° for the reaction is –110 kJ/mol (–27 kcal/mol).

b. Give the equation for the reverse reaction.

c. What is the activation energy for the reverse reaction?

Textbook Question

Draw a reaction-energy diagram for a two-step endothermic reaction with a rate-limiting second step.

Textbook Question

Given the reaction coordinate diagram for the reaction of A to form G, answer the following questions:

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a. How many intermediates are formed in the reaction?

b. Which letters represent transition states?

c. What is the fastest step in the reaction?

d. Which is more stable: A or G?

e. Does A or E form faster from C?

f. Which is the more stable intermediate?

Textbook Question

Draw a reaction coordinate diagram for the following reaction in which C is the most stable and B the least stable of the three species and the transition state going from A to B is more stable than the transition state going from B to C:

a. How many intermediates are there?

b. How many transition states are there?

c. Which step has the greater rate constant in the forward direction?

d. Which step has the greater rate constant in the reverse direction?

Textbook Question

a. Which step in the reaction coordinate diagram shown here has the greatest free energy of activation in the forward direction?

b. Is the first-formed intermediate more apt to revert to reactants or go on to form products?

c. Which step is the rate-determining step of the reaction?

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Textbook Question

Draw a reaction coordinate diagram for a one step reaction that has the following values of E_a and ∆H. (b) E_a = 2 kcal/mol ; ∆H° = -17 kcal/mol

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