Which of the following has longest C-O bond?

Options

A.
B.
C.
D.

Explanation

To determine which of the given compounds has the longest carbon-oxygen (C-O) bond, we need to analyze the types of bonds present in each compound and their hybridization states. Here's a step-by-step solution:

### Step 1: Identify the Bond Types
- **Single Bond**: A single bond between carbon and oxygen (C-O) will be the longest bond due to the lack of additional electron sharing.
- **Double Bond**: A double bond (C=O) will be shorter than a single bond because of increased electron sharing and stronger attraction between the atoms.

### Step 2: Analyze Each Compound
1. **Compound A**: Contains a C=O double bond.
- The presence of a double bond indicates a shorter bond length.

2. **Compound B**: Contains a C=O double bond but also has resonance structures that can lead to a single bond character due to delocalization of electrons.
- The resonance can lead to longer bond lengths compared to a pure double bond.

3. **Compound C**: Similar to Compound A, it contains a C=O double bond.
- Again, this indicates a shorter bond length.

### Step 3: Evaluate Resonance Effects
- **Resonance**: In Compound B, the resonance structures allow for the possibility of the C-O bond having some single bond character, which can increase the bond length compared to a pure double bond.
- The more resonance structures that can be drawn, the more delocalization of electrons occurs, which can lead to longer bond lengths.

### Step 4: Compare Conjugation
- In Compound B, there is significant conjugation involving multiple atoms, which can further stabilize the structure and increase the bond length.
- In contrast, Compounds A and C have less conjugation, leading to shorter bond lengths.

### Step 5: Conclusion
Based on the analysis, the compound with the longest C-O bond is **Compound B**, due to the resonance and conjugation effects that contribute to a longer bond length compared to the other compounds.

### Final Answer
**The compound with the longest C-O bond is Compound B.**