Number of acidic hydrogen atoms in but-1-yne is

Options

A. `1`
B. `2`
C. `3`
D. `4`

Answer

To determine the number of acidic hydrogen atoms in but-1-yne, we will follow these steps:

### Step 1: Understand the Structure of But-1-yne
But-1-yne is an alkyne with the molecular formula C4H6. Its structure can be represented as follows:

```
H H
\ /
C ≡ C
/ \
H C - H
|
H
```

In this structure, there is a triple bond between the first two carbon atoms.

### Step 2: Identify the Types of Hydrogen Atoms
In organic compounds, hydrogen atoms can be classified based on their attachment to carbon atoms:
- **Acidic Hydrogen**: Hydrogen atoms that can be easily removed as protons (H+).
- **Non-acidic Hydrogen**: Hydrogen atoms that are not easily removed.

### Step 3: Analyze the Hybridization of Carbon Atoms
In but-1-yne:
- The first two carbon atoms (C1 and C2) involved in the triple bond are sp hybridized.
- The other two carbon atoms (C3 and C4) are sp2 hybridized.

### Step 4: Determine the Acidity of Hydrogen Atoms
- The acidic hydrogen atom is typically found on sp hybridized carbon atoms because they have a higher s-character (50%) compared to sp2 (33%) or sp3 (25%).
- In but-1-yne, the hydrogen attached to the sp hybridized carbon (C1) is acidic.

### Step 5: Count the Acidic Hydrogen Atoms
From the structure of but-1-yne, we can see:
- There is **one acidic hydrogen** on the sp hybridized carbon (C1).
- The hydrogens on the sp2 hybridized carbons (C3 and C4) are not acidic.

### Conclusion
Therefore, the number of acidic hydrogen atoms in but-1-yne is **1**.

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