How many `sigma and pi` bonds are there in the molecule of tetracyanoethene ?
`(NC)_2 C = C (CN)_2`

Options

A. `9 sigma, 7 pi`
B. `5 sigma, 9 pi`
C. `5 sigma, 8 pi`
D. `9 sigma, 9 pi`

Explanation

To determine the number of sigma (σ) and pi (π) bonds in tetracyanoethene (NC)₂C=C(CN)₂, we can follow these steps:

### Step 1: Draw the Structure
Tetracyanoethene has the following structure:
```
N≡C
|
C=C
|
C≡N
```
In this structure, we can see that there are two cyano (CN) groups attached to each carbon atom of the double bond.

### Step 2: Identify the Bonds
1. **Double Bond (C=C)**:
- Contains 1 sigma bond and 1 pi bond.

2. **Triple Bonds (C≡N)**:
- Each cyano group (C≡N) contains 1 sigma bond and 2 pi bonds.
- Since there are 2 cyano groups, this contributes:
- 2 sigma bonds (1 for each C≡N)
- 4 pi bonds (2 for each C≡N)

### Step 3: Count All Bonds
Now, let's summarize the bonds:
- From the C=C double bond:
- 1 σ bond
- 1 π bond

- From the two C≡N triple bonds:
- 2 σ bonds (1 for each C≡N)
- 4 π bonds (2 for each C≡N)

### Step 4: Total Count
Now, we can add up the total number of sigma and pi bonds:
- **Total σ bonds**:
- From C=C: 1 σ bond
- From C≡N: 2 σ bonds
- Total σ bonds = 1 + 2 = 3 σ bonds

- **Total π bonds**:
- From C=C: 1 π bond
- From C≡N: 4 π bonds
- Total π bonds = 1 + 4 = 5 π bonds

### Final Answer
- Total σ bonds = 3
- Total π bonds = 4

Thus, in tetracyanoethene, there are **3 sigma bonds and 4 pi bonds**.