In general boiling point of covalent compounds is affect due to increasing molecular weight and hydrogen bonding. Thus it is obversed that the boiling point of octanol is greater that water while that of methanol is lesser than water. The other properties which are considerably affected due to hydrogen bond formation are acidic nature, melting point, anamalous behaviour of water below `4^(@)C`., It is therefore concluded that hydrogen bonding palys a vutal role in explaning many observable facts.
Q. `K_(a_(2))` of maleic acid is lesser than `K_(a_(2))` of fumaric acid due to:

Options

A. Intramolecular hydrogen bonding in the formed after one proton removal in fumaric acid
B. Intermolecular hydrogen bonding in the ion formed after one proton removal in maleic acid
C. Intramolecular hydrogen bonding in the ion formed after one proton removal in maleic acid
D. Intermolecular hydrogen bonding in the ion formed after one proton removal in fumaric acid

Answer

To understand why \( K_{a2} \) of maleic acid is lesser than \( K_{a2} \) of fumaric acid, we need to analyze the structures and bonding in both acids. Here is a step-by-step solution:

### Step 1: Identify the Structures of Maleic and Fumaric Acid
- Maleic acid is the cis isomer of butenedioic acid, meaning both carboxylic acid groups (-COOH) are on the same side of the double bond.
- Fumaric acid is the trans isomer, meaning the carboxylic acid groups are on opposite sides of the double bond.

**Hint:** Look at the molecular geometry to understand how the position of functional groups affects interactions.

### Step 2: Understand Acid Dissociation Constants
- The acid dissociation constant \( K_a \) measures the strength of an acid in solution. A higher \( K_a \) indicates a stronger acid that dissociates more readily.
- \( K_{a2} \) refers to the dissociation constant for the second proton being removed from the acid.

**Hint:** Remember that the stability of the resulting anion after deprotonation plays a crucial role in determining the \( K_a \) values.

### Step 3: Analyze the Anion Formation
- When maleic acid loses its first proton, it forms an anion. Due to the proximity of the two carboxylic acid groups, intramolecular hydrogen bonding can occur within the same molecule, stabilizing the anion.
- In contrast, when fumaric acid loses its first proton, the resulting anion does not benefit from such intramolecular hydrogen bonding because the carboxylic acid groups are far apart.

**Hint:** Consider how hydrogen bonding affects the stability of the anions formed after deprotonation.

### Step 4: Compare Stability of Anions
- The anion formed from maleic acid is more stable due to intramolecular hydrogen bonding, which reduces the energy of the anion.
- The anion from fumaric acid, lacking this stabilizing interaction, is less stable.

**Hint:** Stability of anions is a key factor in determining the ease of losing a proton.

### Step 5: Conclusion on \( K_{a2} \) Values
- Since the anion from maleic acid is more stable due to intramolecular hydrogen bonding, maleic acid is less likely to lose its second proton compared to fumaric acid, which can lose its second proton more easily.
- Therefore, \( K_{a2} \) of maleic acid is less than \( K_{a2} \) of fumaric acid.

**Final Answer:** \( K_{a2} \) of maleic acid is lesser than \( K_{a2} \) of fumaric acid due to intramolecular hydrogen bonding in the ion formed after one proton removal in maleic acid.