Question

$K{a}_2$ of Maleic acid is lesser than $K{a}_2$ of fumaric acid due to:

• A. Intramolecular hydrogen bonding in the ion formed after one proton removal in fumaric acid
• B. Intramolecular hydrogen bonding in the ion formed after one proton removal in maleic acid
• C. Intermolecular 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 1

The correct option is B Intramolecular hydrogen bonding in the ion formed after one proton removal in maleic acid

Since after deprotonating the first time, maleic acid forms a stable anion, while fumaric acid cannot, ${Ka}_1$of maleic is higher than of fumaric. For the same reason, ${Ka}_2$ of fumaric acid is higher than of maleic.
When maleic acid loses hydrogen ion, then it forms a very strong intra-hydrogen bond so the acid is more stable and strong also. Also it contains two carboxyl groups on both sides so it is more stable while in fumaric acid, the carboxyl groups are at opposite ends.
conclusion: hence the option (B) is correct.