In the following sets of resonance forms, label the major and minor contributors and state which structures would be of equal energy. Add any missing resonance forms.
`[CH_(3)-overset(O^(-))overset(|)C = CH - overset(+)CH - CH_(3) hArr CH_(3) - underset(+)overset(O^(-))overset(|) C - CH = CH - CH_(3)]`

Answer

To analyze the given resonance forms and determine the major and minor contributors, we will follow these steps:

### Step 1: Identify the Resonance Structures
The two resonance structures provided are:
1. **Structure 1**: \( CH_3 - C^{(-)} = CH - C^{(+)} - CH_3 \)
2. **Structure 2**: \( CH_3 - C^{(+)} - C = CH - CH_3^{(-)} \)

### Step 2: Draw the Missing Resonance Form
To find any missing resonance forms, we can consider the movement of electrons. By shifting the double bond and the charges, we can derive a new resonance structure:
- **Missing Structure**: \( CH_3 - C = C^{(-)} - CH^{(+)} - CH_3 \)

### Step 3: Analyze Stability of Resonance Structures
To determine which structure is the major contributor, we need to evaluate their stability based on the following criteria:
- **Charge Separation**: Structures with less charge separation are generally more stable.
- **Electronegativity**: Negative charges should ideally reside on more electronegative atoms (like oxygen).
- **Proximity of Opposite Charges**: Structures where opposite charges are close to each other are more stable.

1. **Structure 1** has a negative charge on carbon and a positive charge on another carbon, leading to charge separation.
2. **Structure 2** has a positive charge on carbon and a negative charge on another carbon, but the charges are closer together.

### Step 4: Determine Major and Minor Contributors
- **Major Contributor**: Structure 2 is the major contributor because it has a closer proximity of opposite charges, which stabilizes the structure.
- **Minor Contributor**: Structure 1 is the minor contributor due to greater charge separation.

### Step 5: Identify Equal Energy Structures
The missing resonance form can also be considered of equal energy to the other two structures, as it is derived from the same molecule through valid resonance electron movement.

### Summary of Contributors:
- **Major Contributor**: Structure 2
- **Minor Contributor**: Structure 1
- **Equal Energy Structure**: The missing structure derived from the resonance forms.