Which one of the following is strongest acid

Options

A. 2 - chloropentanoic acid
B. 3 - chloropentanoic acid
C. 5 - chloropentanoic acid
D. 4 - chloropentanoic acid

Answer

To determine which of the given compounds is the strongest acid, we need to analyze the structure of each chloropentanoic acid and the effects of the chlorine substituent on acidity.

### Step 1: Identify the compounds
The compounds in question are:
1. 2-chloropentanoic acid
2. 3-chloropentanoic acid
3. 4-chloropentanoic acid
4. 5-chloropentanoic acid

### Step 2: Understand the effect of chlorine on acidity
Chlorine is an electronegative atom, and its presence can influence the acidity of carboxylic acids. The more electronegative substituents that are closer to the carboxylic acid group (–COOH), the stronger the acid will be due to the stabilization of the negative charge on the conjugate base (the carboxylate ion) after deprotonation.

### Step 3: Analyze each compound
- **2-chloropentanoic acid**: The chlorine is on the second carbon, one carbon away from the carboxylic acid group.
- **3-chloropentanoic acid**: The chlorine is on the third carbon, two carbons away from the carboxylic acid group.
- **4-chloropentanoic acid**: The chlorine is on the fourth carbon, three carbons away from the carboxylic acid group.
- **5-chloropentanoic acid**: The chlorine is on the fifth carbon, four carbons away from the carboxylic acid group.

### Step 4: Determine the strongest acid
The strongest acid will be the one where the chlorine is closest to the carboxylic acid group, as it will have a greater effect on stabilizing the negative charge of the conjugate base.

- **2-chloropentanoic acid** has the chlorine closest to the –COOH group, followed by **3-chloropentanoic acid**, **4-chloropentanoic acid**, and finally **5-chloropentanoic acid** which has the chlorine furthest away.

### Conclusion
Therefore, **2-chloropentanoic acid** is the strongest acid among the options provided.