Use the four compounds shown below to answer the following questions:
a. Why are the ortho-halo-substituted benzoic acids stronger acids than benzoic acid?

Verified step by step guidance

1. Identify the compounds: A) benzoic acid, B) 2-nitrobenzoic acid, C) 3-nitrobenzoic acid, D) 4-nitrobenzoic acid.
2. Understand that the nitro group (-NO2) is an electron-withdrawing group, which stabilizes the carboxylate ion formed after deprotonation.
3. Recognize that the ortho position (2-nitrobenzoic acid) allows for intramolecular hydrogen bonding, which further stabilizes the carboxylate ion.
4. Compare the acidity: ortho-nitrobenzoic acid is more acidic than benzoic acid due to the electron-withdrawing effect and possible intramolecular hydrogen bonding.
5. Conclude that the increased acidity of ortho-nitrobenzoic acid is due to both resonance stabilization and intramolecular interactions.

Key Concepts

Acidity and Acid Strength

Acidity refers to the ability of a compound to donate protons (H+) in solution. The strength of an acid is determined by its dissociation constant (Ka), which indicates how completely it ionizes in water. Stronger acids have higher Ka values, meaning they release protons more readily. In the context of benzoic acid and its derivatives, substituents can influence acidity by stabilizing or destabilizing the conjugate base formed after deprotonation.

Inductive Effect

The inductive effect is the electron-withdrawing or electron-donating influence of substituents on a molecule through sigma bonds. Electron-withdrawing groups, such as nitro (NO2), can stabilize the negative charge on the conjugate base of an acid, thereby increasing its acidity. In ortho-substituted benzoic acids, the proximity of the nitro group enhances this effect, making these acids stronger than benzoic acid itself.

Resonance Stabilization

Resonance stabilization occurs when a molecule can be represented by multiple valid Lewis structures, allowing for the delocalization of electrons. In the case of nitro-substituted benzoic acids, the resonance structures can help distribute the negative charge of the conjugate base more effectively. This delocalization further stabilizes the conjugate base, contributing to the increased acidity of ortho-nitrobenzoic acid compared to benzoic acid.