Which carbon atoms are most susceptible to nucleophilic attack?
`underset((A))(CH_(3))-underset((B))(CH)=underset(C )(CH)-overset(O)overset(||)underset(D)C-CH_(3)`

Options

A. A and B
B. B and C
C. B and D
D. A and D

Explanation

To determine which carbon atoms are most susceptible to nucleophilic attack in the given structure, we need to analyze the molecular structure and identify the electrophilic centers.

### Step-by-Step Solution:

1. **Identify the Structure**: The structure given is:
```
CH3 - CH = CH - C(=O) - CH3
```
Here, we have a carbon chain with a carbonyl group (C=O) present.

2. **Recognize Electrophilic Centers**: In organic chemistry, nucleophiles are attracted to electrophilic centers, which are typically carbon atoms bonded to electronegative atoms (like oxygen) or involved in double bonds. The carbonyl carbon (C=O) is a prime electrophilic site due to the polarization of the C=O bond.

3. **Analyze Each Carbon**:
- **Carbon A (CH3)**: This carbon is not electrophilic as it is bonded to hydrogens and is part of a methyl group.
- **Carbon B (CH)**: This carbon is part of a double bond (alkene) and can be somewhat electrophilic, but not as much as the carbonyl carbon.
- **Carbon C (CH)**: This carbon is also part of a double bond and is adjacent to the carbonyl carbon, making it somewhat electrophilic.
- **Carbon D (C=O)**: This carbon is bonded to an oxygen atom with a double bond, making it highly electrophilic due to the significant polarization of the bond.

4. **Determine Susceptibility**: The carbon atom that is most susceptible to nucleophilic attack is the carbonyl carbon (Carbon D) because it has a partial positive charge due to the electronegativity of the oxygen atom.

5. **Conclusion**: Therefore, the carbon atom that is most susceptible to nucleophilic attack is **Carbon D** (the carbon in the carbonyl group).

### Final Answer:
The carbon atom most susceptible to nucleophilic attack is **Carbon D** (C=O).