Which of the following order is expected to be correct ?

Options

A. `pK_(a)(ClCH_(2)COOH) gt pK_(a)(CH_(3)COOH) lt pK_(a) (CH_(3)CH_(2)COOH)`
B. `pK_(a)(ClCH_(2)COOH) lt pK_(a)(CH_(3)COOH) lt pK_(a) (CH_(3)CH_(2)COOH)`
C. `pK_(a)(ClCH_(2)COOH) gt pK_(a)(CH_(3)COOH) gt pK_(a) (CH_(3)CH_(2)COOH)`
D. `pK_(a)(ClCH_(2)COOH) lt pK_(a)(CH_(3)COOH) gt pK_(a) (CH_(3)CH_(2)COOH)`

Answer

To determine the correct order of acidity among the given compounds, we need to analyze the structures and the effects of substituents on their acidic strength. Here’s a step-by-step solution:

### Step 1: Identify the Compounds
The compounds given are:
1. \( \text{CH}_3\text{CH}_2\text{COH} \) (ethanol)
2. \( \text{CH}_3\text{COOH} \) (acetic acid)
3. \( \text{ClCH}_2\text{CH}_2\text{COH} \) (chloroethanol)

### Step 2: Understand the pKa Values
The pKa value is a measure of the acidity of a compound; lower pKa values indicate stronger acids. The acidic strength is influenced by the stability of the conjugate base formed after deprotonation.

### Step 3: Analyze Each Compound
1. **For \( \text{CH}_3\text{CH}_2\text{COH} \)**:
- The \( \text{CH}_2 \) group exhibits a +I (inductive) effect, which donates electron density. This reduces the stability of the conjugate base (carboxylate ion), leading to a higher pKa and lower acidity.

2. **For \( \text{CH}_3\text{COOH} \)**:
- Acetic acid has a carboxylic acid functional group, which is a stronger acid compared to alcohols. The conjugate base is stabilized by resonance, leading to a lower pKa value.

3. **For \( \text{ClCH}_2\text{CH}_2\text{COH} \)**:
- The chlorine atom has a -I (inductive) effect, pulling electron density away from the molecule. This stabilizes the conjugate base, resulting in a lower pKa and higher acidity.

### Step 4: Compare the Acidity
Based on the analysis:
- \( \text{ClCH}_2\text{CH}_2\text{COH} \) will have the lowest pKa (strongest acid).
- \( \text{CH}_3\text{COOH} \) will have a moderate pKa.
- \( \text{CH}_3\text{CH}_2\text{COH} \) will have the highest pKa (weakest acid).

### Step 5: Write the Correct Order
Thus, the expected order of acidity from strongest to weakest is:
\[ \text{ClCH}_2\text{CH}_2\text{COH} < \text{CH}_3\text{COOH} < \text{CH}_3\text{CH}_2\text{COH} \]

### Final Answer
The correct order of acidity is:
\[ \text{ClCH}_2\text{CH}_2\text{COH} < \text{CH}_3\text{COOH} < \text{CH}_3\text{CH}_2\text{COH} \]

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