Which of the following resonating structures of `1`-methoxy-`1`,`3`-butadiene is least stable?

Options

A. `overset(Θ)(CH_(2))-CH=CH-CH=overset(o+)(O)-CH_(3)`
B. `CH_(2)=CH-overset(Θ)(CH)-CH=overset(o+)(O)-CH_(3)`
C. `overset(Θ)(CH_(2))-Coverset(o+)(H)-CH=CH-O-CH_(3)`
D. `CH_(2)=CH-overset(Θ)(CH)-overset(o+)(CH)-O-CH_(3)`

Explanation

To determine which resonating structure of 1-methoxy-1,3-butadiene is least stable, we can follow these steps:

### Step 1: Draw the Structure of 1-Methoxy-1,3-butadiene
1. **Identify the components**: 1-methoxy-1,3-butadiene consists of a butadiene chain (four carbon atoms with alternating double bonds) and a methoxy group (-OCH3) attached to the first carbon.
2. **Draw the structure**: The structure can be represented as follows:
```
CH2=CH-CH=CH-OCH3
```

### Step 2: Identify Resonating Structures
1. **Draw possible resonating structures**: Resonating structures can be drawn by shifting the double bonds and lone pairs while keeping the overall connectivity of the molecule intact.
2. **List the structures**: Let's denote the resonating structures as A, B, C, and D.

### Step 3: Analyze Stability of Each Structure
1. **Check for complete octets**:
- Structures A and B have all atoms with complete octets.
- Structures C and D have positive charges on carbon atoms, indicating incomplete octets.

2. **Evaluate charge distribution**:
- In structure C, the positive charge is on a carbon atom without any adjacent lone pairs to stabilize it.
- In structure D, the positive charge can be stabilized by the lone pairs on the oxygen atom through resonance.

### Step 4: Determine the Least Stable Structure
1. **Compare C and D**: Since structure D has the potential for resonance stabilization due to the adjacent lone pairs on oxygen, it is more stable than structure C.
2. **Conclusion**: Structure C is the least stable because it has a positive charge on a carbon atom with no resonance stabilization available.

### Final Answer:
The least stable resonating structure of 1-methoxy-1,3-butadiene is **C**.

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