Which of the following is the strongest acid ?

Options

A. `CH_3 COOH `
B. `CH_3 CHCl COOH`
C. `CH_3 CH_2 COOH `
D. `CH_2 ClCH_2 COOH`

Answer

To determine which of the given acids is the strongest, we need to analyze the stability of the conjugate bases formed when these acids donate a proton (H+). The strength of an acid is directly related to the stability of its conjugate base. Here's a step-by-step breakdown of the solution:

### Step 1: Identify the acids and their conjugate bases
- Let's denote the acids as A, B, C, and D. When each acid donates a proton (H+), it forms a conjugate base (A-, B-, C-, D-).

### Step 2: Analyze the conjugate bases
- The strength of the acid depends on how stable the conjugate base is. The more stable the conjugate base, the stronger the acid.

### Step 3: Consider the effects of substituents
- Each acid has different substituents that can affect the stability of the conjugate base:
- Alkyl groups (like CH3) have a +I (inductive) effect, which increases electron density and can destabilize the negative charge on the conjugate base.
- Electron-withdrawing groups (like Cl) have a -I effect, which decreases electron density and can stabilize the negative charge on the conjugate base.

### Step 4: Compare the stability of the conjugate bases
- For the acid with the alkyl group (let's say option C), the +I effect from the alkyl group increases electron density, making the conjugate base less stable.
- For the acid with the Cl substituent (option B), the -I effect from Cl decreases electron density, stabilizing the conjugate base.

### Step 5: Evaluate the distance effect
- The distance of the electron-withdrawing group from the negative charge also matters. If the -I effect is further away, it will have less influence. In this case, the Cl is closer to the negative charge in option B, enhancing its stabilizing effect.

### Conclusion
- Based on the analysis, the conjugate base of option B is the most stable due to the strong -I effect of Cl, making option B the strongest acid.

### Final Answer
- The strongest acid among the given options is **B**.

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