Number of `p pi- p pi` , double bond in given compound `CN-CH = CH-CN` is ____.

Answer

To determine the number of `p pi - p pi` double bonds in the compound `CN-CH=CH-CN`, we will analyze the structure and bonding of the compound step by step.

### Step 1: Identify the structure of the compound
The compound `CN-CH=CH-CN` can be represented as follows:
- The `CN` groups indicate that there are carbon and nitrogen atoms connected by a triple bond.
- The `CH=CH` indicates a double bond between two carbon atoms.

### Step 2: Analyze the bonding in the compound
1. **Triple Bond (C≡N)**:
- In the `CN` group, the carbon and nitrogen are connected by a triple bond.
- A triple bond consists of one sigma bond and two pi bonds.
- Since both carbon and nitrogen are in the second period, the pi bonds formed are `p pi - p pi` bonds.

2. **Double Bond (C=C)**:
- The double bond between the two carbon atoms (in `CH=CH`) consists of one sigma bond and one pi bond.
- The pi bond formed here is also a `p pi - p pi` bond because both atoms are carbon.

### Step 3: Count the number of `p pi - p pi` bonds
- From the two `CN` groups (triple bonds), we have:
- 2 pi bonds from each `CN` group, contributing a total of 2 `p pi - p pi` bonds from one `CN` and another 2 from the other `CN`. This gives us a total of 4 `p pi - p pi` bonds from the two triple bonds.

- From the double bond (C=C), we have:
- 1 pi bond contributing 1 `p pi - p pi` bond.

### Step 4: Total number of `p pi - p pi` bonds
- Total from triple bonds: 4
- Total from double bond: 1
- Therefore, the total number of `p pi - p pi` bonds in the compound `CN-CH=CH-CN` is:
\[ 4 + 1 = 5 \]

### Final Answer
The number of `p pi - p pi` double bonds in the compound `CN-CH=CH-CN` is **5**.

---