Between maleic acid fumaric acids, `K_(a_(1))` is more for

Options

A. maleic acid
B. fumaric acid
C. both equal
D. cannot be predicted

Answer

To determine which acid, maleic acid or fumaric acid, has a higher dissociation constant \( K_{a1} \), we need to analyze the structures and the stability of the conjugate bases formed after the acids lose a proton (H⁺).

### Step-by-Step Solution:

1. **Identify the Structures**:
- Maleic acid (cis-isomer) has two carboxylic acid groups (–COOH) on adjacent carbon atoms, and they are positioned on the same side of the double bond.
- Fumaric acid (trans-isomer) also has two carboxylic acid groups, but they are on opposite sides of the double bond.

2. **Dissociation of Acids**:
- When maleic acid dissociates, it loses a proton from one of its carboxylic acid groups, forming a conjugate base.
- The same occurs for fumaric acid.

3. **Stability of Conjugate Bases**:
- The stability of the conjugate base is crucial in determining the acidity of the acid. The more stable the conjugate base, the stronger the acid (higher \( K_a \)).
- In maleic acid, after losing a proton, the resulting anion can participate in **intramolecular hydrogen bonding**. This stabilizes the negative charge on the conjugate base.
- In fumaric acid, after losing a proton, the resulting anion experiences **intermolecular hydrogen bonding**. While this also stabilizes the negative charge, it is generally less effective than intramolecular hydrogen bonding.

4. **Comparison of Hydrogen Bonding**:
- Intramolecular hydrogen bonding (as seen in maleic acid) is typically stronger and more stabilizing than intermolecular hydrogen bonding (as seen in fumaric acid). This is because the intramolecular interactions are more favorable due to proximity.
- Therefore, the conjugate base of maleic acid is more stabilized compared to that of fumaric acid.

5. **Conclusion**:
- Since the conjugate base of maleic acid is more stable due to intramolecular hydrogen bonding, maleic acid has a higher dissociation constant \( K_{a1} \) compared to fumaric acid.

### Final Answer:
**Maleic acid has a higher \( K_{a1} \) than fumaric acid.**