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

Options

A. `overset (Ө) C H_2 - CH = CH - CH = overset (oplus) O - CH_3`
B. `CH_2 = CH- overset (Ө) CH - CH = overset (oplus) O - CH_3`
C. `overset (Ө) CH_2 - overset (oplus) CH - CH = CH - O - CH_3`
D. `CH_2 = CH - overset (Ө) C H - overset (oplus) C H - O - CH_3`

Explanation

To determine which resonating structure of 1-methoxy-1,3-butadiene is least stable, we need to analyze the stability of each resonating structure based on the octet rule and the presence of charges.

### Step-by-Step Solution:

1. **Draw the Structure of 1-Methoxy-1,3-butadiene**:
- The molecular formula indicates that we have a butadiene (4 carbon atoms with alternating double bonds) and a methoxy group (-OCH3) attached to the first carbon.
- The structure can be represented as:
```
CH2=CH-CH=CH-OCH3
```

2. **Identify Resonating Structures**:
- The resonating structures can be drawn by moving the electrons in the double bonds and the lone pairs on oxygen.
- For example:
- **Structure A**: All atoms have complete octets.
- **Structure B**: Similar to A but with a different arrangement of double bonds.
- **Structure C**: Contains a positive charge on a carbon atom with an incomplete octet.
- **Structure D**: Also has a positive charge but is stabilized by the methoxy group.

3. **Evaluate Stability Based on Octet Rule**:
- Structures A and B have all atoms with complete octets, making them more stable.
- Structures C and D have incomplete octets, which generally leads to lower stability.

4. **Analyze Charge Distribution**:
- In Structure D, the positive charge on carbon is compensated by the lone pair of electrons from the methoxy group, providing some stability.
- In Structure C, there is no such stabilization for the positive charge, making it less stable.

5. **Conclusion**:
- Based on the analysis, Structure C is the least stable resonating structure of 1-methoxy-1,3-butadiene due to the incomplete octet and lack of stabilization for the positive charge.

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