Step 1: Understanding the Question:
The question asks to compare the acidic strength of acetic acid and its various chlorinated derivatives and identify the strongest one.
Step 2: Key Formula or Approach:
The strength of a carboxylic acid (\(\text{R-COOH}\)) is determined by the stability of its conjugate base, the carboxylate anion (\(\text{R-COO}^-\)). Any factor that stabilizes this anion will increase the acidity. Electron-withdrawing groups (EWGs) attached to the R group stabilize the anion through the negative inductive effect (\(-I\) effect) by delocalizing the negative charge.
Step 3: Detailed Explanation:
Let's analyze the groups attached to the \(\text{-COOH}\) group in each acid:
- Acetic acid (\(\text{CH}_3\text{COOH}\)): The methyl group (\(-\text{CH}_3\)) is an electron-donating group, which slightly destabilizes the anion. It is the weakest acid in this list.
- Chloroacetic acid (\(\text{ClCH}_2\text{COOH}\)): Chlorine is a highly electronegative atom, making it a strong electron-withdrawing group. It pulls electron density away from the carboxylate anion, stabilizing it and making the acid stronger than acetic acid.
- Dichloroacetic acid (\(\text{Cl}_2\text{CHCOOH}\)): This molecule has two chlorine atoms. The inductive effect is additive, so two Cl atoms withdraw more electron density than one. This makes dichloroacetic acid stronger than chloroacetic acid.
- Trichloroacetic acid (\(\text{Cl}_3\text{CCOOH}\)): With three chlorine atoms, the electron-withdrawing inductive effect is at its maximum for this series. This provides the most stabilization to the conjugate base.
The order of acidity is therefore:
\[ \text{Trichloroacetic acid}>\text{Dichloroacetic acid}>\text{Chloroacetic acid}>\text{Acetic acid} \]
Step 4: Final Answer:
Trichloroacetic acid is the strongest acid among the given compounds due to the powerful cumulative \(-I\) effect of three chlorine atoms.