Carboxylic Acids

The acidic strength of these compounds can be determined based on the substituents attached to the aromatic ring, which influence the electron density and hence the acidity.

• Compound A: Has two groups, which are electron-withdrawing groups that increase the acidity.
• Compound B: Has a group, which is an extremely strong electron-withdrawing group, significantly increasing the acidity, but still lower than the combination of two groups in A.
• Compound C: Has an group, which is electron-donating and thus lowers the acidity.
• Compound D: Has a group, another electron-donating group, further reducing the acidity.

Thus, the correct order of acidity is , where compound A is the most acidic, followed by C, D, and B.

Step 1: Anhydride Formation.
When heating dicarboxylic acids, they typically undergo dehydration to form anhydrides. However, the presence of bulky substituents on the carboxyl groups can hinder this process.

Step 2: Analysis of Options.
- (1) Glutaric acid: Glutaric acid can form an anhydride upon heating.
- (2) Maleic acid: Maleic acid can also undergo dehydration to form an anhydride.
- (3) Dimethyl succinic acid: Dimethyl succinic acid, with methyl groups on the carboxyl groups, still readily forms anhydride.
- (4) Dimethyl malonic acid: The bulky methyl groups on the carboxyl groups prevent the formation of an anhydride. Therefore, this acid does not readily form anhydride on heating.

Step 3: Conclusion.
Thus, the correct answer is (4) Dimethyl malonic acid.

Final Answer: