Which acid in each of the following pairs is stronger?
c.
d.

Verified step by step guidance

1. Step 1: Analyze the molecular structures in pair (c). The first molecule (i) is cyclohexanecarboxylic acid, while the second molecule (ii) is cyclohexanecarboxylic acid with a ketone group attached to the ring. The ketone group is an electron-withdrawing group.
2. Step 2: Understand the effect of electron-withdrawing groups on acidity. Electron-withdrawing groups stabilize the conjugate base by delocalizing the negative charge, making the acid stronger.
3. Step 3: Compare the two molecules in pair (c). The ketone group in molecule (ii) increases the acidity of the carboxylic acid group compared to molecule (i), which lacks the electron-withdrawing ketone group.
4. Step 4: Analyze the molecular structures in pair (d). The first molecule (i) is cyclopentanecarboxylic acid, while the second molecule (ii) is cyclopentanecarboxylic acid with an amine group (-NH) attached to the ring. The amine group is an electron-donating group.
5. Step 5: Understand the effect of electron-donating groups on acidity. Electron-donating groups destabilize the conjugate base by increasing electron density, making the acid weaker. Therefore, molecule (i) is stronger than molecule (ii) in pair (d).

Key Concepts

Acidity and pKa

Acidity refers to the ability of a compound to donate a proton (H+) in solution. The strength of an acid is often measured by its pKa value; lower pKa values indicate stronger acids. Understanding the relationship between structure and acidity is crucial, as factors like electronegativity and resonance can significantly influence a compound's ability to stabilize the negative charge of its conjugate base.

Resonance Stabilization

Resonance stabilization occurs when a molecule can be represented by multiple valid Lewis structures, allowing for the delocalization of electrons. This delocalization can stabilize the conjugate base formed after deprotonation, making the original acid stronger. In the context of the question, comparing the resonance effects in the given acid structures will help determine which acid is stronger.

Inductive Effect

The inductive effect refers to the electron-withdrawing or electron-donating effects transmitted through sigma bonds in a molecule. Electronegative atoms or groups can stabilize the negative charge of a conjugate base through the inductive effect, enhancing acidity. Analyzing the presence of such groups in the acid structures presented will aid in assessing their relative strengths.