Practice Problems on Carboxylic Acids

Problem 1: Decarboxylation

• Given: Identify compound that undergoes decarboxylation upon heating.
• Key Concept: Decarboxylation occurs with beta-keto acids and beta-dicarboxylic acids.
• Definition: Decarboxylation involves a cyclic transition state allowing hydrogen transfer and CO2 loss.
• Criteria:
  • Beta-keto acid: One carbon between a ketone and a carboxyl group.
  • Beta-dicarboxylic acid: One carbon between two carboxyl groups.
• Correct Answer: D (A beta-keto acid with one carbon between ketone and carboxyl group).

Problem 2: Boiling Points

• Given: Reason for higher boiling point of carboxylic acids compared to alcohols.
• Choices: Molecular weight, pH, solubility, hydrogen bonding.
• Key Concept: Boiling point depends on intermolecular forces; carboxylic acids have stronger hydrogen bonds due to being more polar.
• Correct Answer: D (Stronger hydrogen bonding in carboxylic acids).

Problem 3: Acidity of Carboxylic Acids

• Given: Identify the most acidic carboxylic acid.
• Criteria: Acidity increases with more and closer electronegative groups.
• Comparison: Halogens at alpha (C) vs. beta (B) positions.
• Correct Answer: B (Two halogens at beta position).

Problem 4: Identification of Soap

• Given: Determine which molecule can be classified as soap.
• Definition: Soap is a salt of a carboxylate anion with a long hydrocarbon chain.
• Criteria: Must have a long hydrocarbon chain and be a carboxylate salt.
• Correct Answer: C (Has long hydrocarbon tail and carboxylate anion).

Problem 5: Oxidation Reaction Product

• Given: Final product of reaction between primary alcohol and chromium trioxide.
• Reagent: Chromium trioxide is a strong oxidizing agent.
• Reaction: Primary alcohol oxidized to carboxylic acid.
• Correct Answer: B (Primary alcohol oxidized to carboxylic acid).

Problem 6: Reactivity of Carboxylic Acids

• Given: Possible one-step reactions of carboxylic acids.
• Products: Esters, amides, alkenes, alcohols.
• Key Concept: Carboxylic acids cannot be converted to alkenes in one step.
• Correct Answer: C (Cannot form alkenes in one step).

Problem 7: Reduction by Lithium Aluminum Hydride

• Given: Product of reducing carboxylic acid using lithium aluminum hydride.
• Reagent: Strong reducing agent.
• Reaction: Carboxylic acid reduces to primary alcohol.
• Correct Answer: D (Reduction to primary alcohol).

Problem 8: Properties of Micelles

• Given: True statement about micelles in hydrophilic environment.
• Composition: Hydrophobic interior, hydrophilic exterior (covered with carboxylate groups).
• Correct Answer: D (Can dissolve non-polar molecules in core).

Problem 9: Esterification Reaction

• Given: Major product of reaction between butanoic acid and one-pentanol with acid catalyst.
• Reaction: Carboxylic acid reacts with alcohol to form ester.
• Correct Answer: D (Forms pentyl butanoate).

Problem 10: Acidity Comparison

• Given: Statements about alpha hydrogen of carboxylic acid.
• Key Points: Alpha hydrogen is less acidic than hydroxy hydrogen and relatively acidic due to resonance stabilization.
• Correct Answer: D (Statements 2 and 3 are true).

Problem 11: Reaction with Sodium Borohydride

• Given: Final product of formic acid with sodium borohydride.
• Reagent: Mild reducing agent, does not reduce carboxylic acid.
• Correct Answer: B (No change, remains formic acid).

Problem 12: Intramolecular Reaction

• Given: Product of intramolecular reaction of 5-amino pentanoic acid.
• Reaction: Intramolecular nucleophilic acyl substitution forms cyclic amide (lactam).
• Correct Answer: C (Forms lactam).

Problem 13: Formation of Anhydride

• Given: Reaction producing butanoic anhydride.
• Reaction: Involves two molecules of butanoic acid.
• Correct Answer: A (Two molecules of butanoic acid).

Problem 14: Favorable Conditions for Nucleophilic Acyl Substitution

• Given: Conditions favoring nucleophilic acyl substitution.
• Key Points: Favored by both basic and acidic solutions, but not by strong base leaving groups.
• Correct Answer: C (Both basic and acidic solutions).

Problem 15: Reaction with Ammonia

• Given: Product of capric acid with ammonia.
• Reaction: Forms amide and water (as leaving group).
• Correct Answer: D (Produces water).

Conclusion

• Practice problem sets help reinforce key concepts about carboxylic acids: decarboxylation, boiling points, acidity, soap formation, oxidation, reduction, esterification, and nucleophilic acyl substitution.
• Emphasis on understanding reaction mechanisms and conditions that favor specific products.