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Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook
Chapter 3, Problem 61b

Give the products of the following acid–base reactions and indicate whether reactants or products are favored at equilibrium.
b. CH3CH2OH + -NH2

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1
Step 1: Identify the acid and base in the reaction. CH3CH2OH (ethanol) acts as the acid because it can donate a proton (H+), and NH2⁻ (amide ion) acts as the base because it can accept a proton.
Step 2: Write the conjugate acid and conjugate base formed after the proton transfer. When CH3CH2OH donates a proton, it forms CH3CH2O⁻ (ethoxide ion). When NH2⁻ accepts a proton, it forms NH3 (ammonia). The reaction can be written as: CH3CH2OH + NH2⁻ ⇌ CH3CH2O⁻ + NH3.
Step 3: Use the pKa values to determine the strength of the acids and bases. The pKa of CH3CH2OH is approximately 16, and the pKa of NH3 is approximately 38. Lower pKa values indicate stronger acids.
Step 4: Compare the pKa values of the acids on both sides of the equilibrium. Since CH3CH2OH (pKa = 16) is a stronger acid than NH3 (pKa = 38), the equilibrium will favor the formation of the weaker acid and base, which are NH3 and CH3CH2O⁻.
Step 5: Conclude that the products (CH3CH2O⁻ and NH3) are favored at equilibrium because the reaction shifts toward the side with the weaker acid and base.

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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 these reactions, acids donate protons while bases accept them. Understanding the nature of the reactants, including their acidity and basicity, is crucial for predicting the products and the direction of the equilibrium.
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The Lewis definition of acids and bases.

pKa and Equilibrium

The pKa value is a measure of the strength of an acid; lower pKa values indicate stronger acids. In acid-base reactions, the equilibrium position can be predicted by comparing the pKa values of the acids and bases involved. The reaction will favor the formation of the weaker acid and base, which corresponds to the higher pKa value.
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The relationship between equilibrium constant and pKa.

Equilibrium Position

The equilibrium position of a reaction indicates the relative concentrations of reactants and products at equilibrium. In acid-base reactions, if the products are favored, it means that the reaction proceeds to the right, forming more products. Conversely, if the reactants are favored, the equilibrium lies to the left, indicating that the original substances are more stable.
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Reactions at the Allylic Position Concept 5