Ch. 2 - Acids and Bases; Functional Groups

Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook

Wade 9th Edition

Ch. 2 - Acids and Bases; Functional Groups

Problem 12c,d

Chapter 2, Problem 12c,d

For each of the following reactions, suggest which solvent(s) would be compatible with the acids and bases involved. (We will ignore any other possible reactions for now.) Your choices of solvents are pentane, diethyl ether, ethanol, water, and ammonia. Refer to Appendix 4 for any needed values of pK_a, or estimate them.
c.
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Identify the nature of the reactants and products in each reaction. In the first reaction, pyrrole (a weak base) reacts with ethylsulfonium ion (a strong acid) to form a pyrrole cation and ethyl sulfide. In the second reaction, sodium amide (a strong base) reacts with tert-butanol (a weak acid) to form ammonia and sodium tert-butoxide.

Consider the polarity and protic/aprotic nature of the solvents. Polar protic solvents like water and ethanol can stabilize ions through hydrogen bonding, while polar aprotic solvents like diethyl ether can stabilize ions through dipole interactions without hydrogen bonding.

For the first reaction, a polar protic solvent like water or ethanol would be suitable as they can stabilize the charged intermediates and products. However, ethanol might be preferred over water to avoid excessive solvation of the pyrrole cation.

For the second reaction, a polar aprotic solvent like diethyl ether or a non-polar solvent like pentane could be used to avoid protonation of the strong base sodium amide. Ammonia could also be a suitable solvent as it is a common solvent for reactions involving sodium amide.

Evaluate the compatibility of the solvents with the reactants and products. Ensure that the chosen solvent does not participate in side reactions or interfere with the desired reaction pathway.

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Key Concepts

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

Solvent Polarity

Solvent polarity is crucial in determining the compatibility of solvents with acids and bases in a reaction. Polar solvents, like water and ethanol, can stabilize charged species through solvation, while non-polar solvents, like pentane, are better suited for reactions involving neutral molecules. Understanding the polarity helps predict solvent effects on reaction rates and equilibria.

Acid-Base Chemistry

Acid-base chemistry involves the transfer of protons between molecules, which is central to many organic reactions. The strength of acids and bases, often measured by pKa values, influences their reactivity and the choice of solvent. Strong acids and bases require solvents that can stabilize ions, while weaker ones may be compatible with less polar solvents.

Solvent Compatibility

Solvent compatibility refers to the ability of a solvent to dissolve reactants and facilitate the desired reaction without interfering. Factors like solvent polarity, boiling point, and chemical inertness are considered. For example, ammonia can act as a base and solvent, while diethyl ether is a common choice for reactions needing a non-polar environment.

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Related Practice

Textbook Question

Ethanol, methylamine, and acetic acid are all amphoteric, reacting as either acids or bases depending on the conditions.

a. Rank ethanol, methylamine, and acetic acid in decreasing order of acidity. In each case, show the equation for the reaction with a generic base (B:⁻) to give the conjugate base.

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Textbook Question

Write equations for the following acid–base reactions. Label the conjugate acids and bases, and show any inductive stabilization. Predict whether the equilibrium favors the reactants or products. Try to do this without using a table of pK_a values, but if you need a hint, you can consult Appendix 4.

g. NaOCH₂CH₃ + Cl₂CHCH₂OH

h. H₂Se + NaNH₂

i. CH₃CHFCOOH + FCH₂CH₂COO^–

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Textbook Question

Write equations for the following acid–base reactions. Label the conjugate acids and bases, and show any inductive stabilization. Predict whether the equilibrium favors the reactants or products. Try to do this without using a table of pKa values, but if you need a hint, you can consult Appendix 4.

j. CF₃CH₂O^– + FCH₂CH₂OH

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Textbook Question

Ethanol, methylamine, and acetic acid are all amphoteric, reacting as either acids or bases depending on the conditions.

b. Rank ethanol, methylamine, and acetic acid in decreasing order of basicity. In each case, show the equation for the reaction with a generic acid (HA) to give the conjugate acid.

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Textbook Question

Write equations for the following acid–base reactions. Label the conjugate acids and bases, and show any inductive stabilization. Predict whether the equilibrium favors the reactants or products. Try to do this without using a table of pKa values, but if you need a hint, you can consult Appendix 4.

a. CH₃CH₂OH + CH₃NH⁻

b. F₃CCOONa + Br₃C—COOH

c. CH₃OH + H₂SO₄

Textbook Question

For each of the following reactions, suggest which solvent(s) would be compatible with the acids and bases involved. (We will ignore any other possible reactions for now.) Your choices of solvents are pentane, diethyl ether, ethanol, water, and ammonia. Refer to Appendix 4 for any needed values of pK_a, or estimate them.

a. CH₃Li + H—C≡C—H → CH₄ + H—C≡CLi

b. CH₃Li + (CH₃)3C—OH → CH₄ + (CH₃)₃C—OLi

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