The number of `sigma` and `pi`-bonds in but-1-en-3-yne are

Options

A. 5 sigma and 5 pi
B. 7 sigma and 3 pi
C. 8 sigma and 2 pi
D. 6 sigma and 4 pi

Answer

To determine the number of sigma (σ) and pi (π) bonds in but-1-en-3-yne, we first need to draw its structural formula based on the name.

### Step 1: Draw the Structure
1. **Identify the Carbon Backbone**: The name "but" indicates that there are 4 carbon atoms.
2. **Identify the Functional Groups**: "1-en" indicates a double bond between the first and second carbon atoms, and "3-yne" indicates a triple bond starting from the third carbon atom.

The structure can be represented as follows:
```
H H
| |
H--C==C--C≡C--H
| |
H H
```

### Step 2: Count the Sigma Bonds
- **Single Bonds**: Each single bond is a sigma bond.
- **Double Bonds**: A double bond consists of one sigma bond and one pi bond.
- **Triple Bonds**: A triple bond consists of one sigma bond and two pi bonds.

Now, let's count the sigma bonds:
- **Between C1 and C2**: 1 sigma bond (in the double bond)
- **Between C2 and C3**: 1 sigma bond (in the double bond)
- **Between C3 and C4**: 1 sigma bond (in the triple bond)
- **Between C1 and H**: 3 sigma bonds (C1 has 3 H atoms)
- **Between C2 and H**: 2 sigma bonds (C2 has 2 H atoms)
- **Between C3 and H**: 1 sigma bond (C3 has 1 H atom)
- **Between C4 and H**: 1 sigma bond (C4 has 1 H atom)

Total sigma bonds:
- 1 (C1-C2) + 1 (C2-C3) + 1 (C3-C4) + 3 (C1-H) + 2 (C2-H) + 1 (C3-H) + 1 (C4-H) = 10 sigma bonds.

### Step 3: Count the Pi Bonds
- **Double Bond (C1=C2)**: 1 pi bond
- **Triple Bond (C3≡C4)**: 2 pi bonds

Total pi bonds:
- 1 (from double bond) + 2 (from triple bond) = 3 pi bonds.

### Final Count
- **Total Sigma Bonds**: 7
- **Total Pi Bonds**: 3

### Answer
The number of sigma (σ) and pi (π) bonds in but-1-en-3-yne are:
- **Sigma Bonds**: 7
- **Pi Bonds**: 3