Which one is the most acidic compound?

Options

A.
B.
C.
D.

Answer

To determine which compound is the most acidic among the given options, we need to analyze the effects of substituents on the acidity of phenolic compounds. Here’s a step-by-step solution:

### Step 1: Identify the Compounds
All the compounds in the question are phenolic compounds, meaning they contain a benzene ring with a hydroxyl (OH) group. The presence of different substituents on the benzene ring will influence their acidity.

### Step 2: Understand Acidity in Phenolic Compounds
Acidity in phenolic compounds is influenced by the ability of the compound to donate a proton (H+). The strength of the O-H bond in the hydroxyl group is crucial; if the bond is weak, the compound can easily release H+, making it more acidic.

### Step 3: Analyze the Effect of Substituents
- **Electron Donating Groups (EDGs)**: These groups, such as -CH3 (methyl), donate electrons to the benzene ring. This donation stabilizes the ring but makes the O-H bond stronger, making it harder to release H+ and thus decreasing acidity.

- **Electron Withdrawing Groups (EWGs)**: Groups like -NO2 (nitro) withdraw electrons from the benzene ring. This withdrawal weakens the O-H bond, making it easier to release H+ and thus increasing acidity.

### Step 4: Compare the Given Options
- **Option A**: Contains a methyl group (-CH3), which is an EDG. This makes it less acidic.
- **Option B**: Is phenol with no substituents, serving as a baseline for acidity.
- **Option C**: Contains one nitro group (-NO2), which is an EWG. This increases acidity compared to phenol.
- **Option D**: Contains three nitro groups. The presence of multiple EWGs significantly increases the acidity of this compound.

### Step 5: Determine the Most Acidic Compound
Since option D has three nitro groups, which are strong electron withdrawing groups, it will be the most acidic among all the options. The presence of multiple EWGs will greatly enhance the ability of the compound to donate H+.

### Conclusion
The most acidic compound among the given options is **Option D** (the compound with three nitro groups).

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