Which of the following carbonyl compounds is most polar ?

Options

A. `C_(2)H_(5)-overset(O)overset("||")C-C_(2)H_(5)`
B. `CH_(3)-overset(O)overset("||")C-CH_(3)`
C. `CH_(3)-overset(O)overset("||")C-H`
D. `H-overset(O)overset("||")C-H`

Explanation

To determine which carbonyl compound is the most polar among the given options, we need to analyze the structure of each compound and the effects of the substituents on the polarity.

### Step-by-Step Solution:

1. **Understanding Polarity**:
- Polarity in carbonyl compounds arises from the difference in electronegativity between carbon (C) and oxygen (O) in the carbonyl group (C=O). The oxygen atom is more electronegative than carbon, resulting in a partial negative charge (δ-) on the oxygen and a partial positive charge (δ+) on the carbon.

2. **Identifying the Substituents**:
- Each carbonyl compound has different substituents attached to the carbonyl carbon. The nature of these substituents (electron-donating or electron-withdrawing) affects the overall polarity of the compound.
- Electron-donating groups (like -C2H5 or -CH3) can reduce the positive charge on the carbonyl carbon, while electron-withdrawing groups can enhance it.

3. **Analyzing Each Option**:
- **Option A**: Contains two ethyl groups (-C2H5). Both groups are electron-donating (inductive effect), which reduces the overall polarity.
- **Option B**: Contains one ethyl group and one methyl group (-C2H5 and -CH3). This is still electron-donating, but slightly less than option A.
- **Option C**: Contains one ethyl group and one hydrogen atom. The ethyl group still donates electrons, but there is no other electron-donating group to counteract the positive charge.
- **Option D**: Contains two hydrogen atoms. There are no electron-donating groups present, which means the positive charge on the carbonyl carbon is maximized, leading to the highest polarity.

4. **Comparing Dipole Moments**:
- The dipole moment (μ) is a measure of polarity and is calculated as μ = Q × d, where Q is the charge and d is the distance between charges.
- In option D, the absence of electron-donating groups leads to a higher charge separation, resulting in a higher dipole moment.

5. **Conclusion**:
- Based on the analysis, option D is the most polar carbonyl compound because it has the highest charge separation due to the absence of electron-donating groups.

### Final Answer:
**Option D is the most polar carbonyl compound.**