Record the following sets of compounds according to increasing `pK_(a) ( = - log Ka)`
1-butyne, 1-butene, butane

Answer

To arrange the compounds 1-butyne, 1-butene, and butane according to increasing pKa values, we need to analyze their acidity based on their structures and hybridization.

### Step-by-Step Solution:

1. **Identify the Compounds**: We have three compounds:
- 1-butyne (C₄H₆) - an alkyne with a triple bond.
- 1-butene (C₄H₈) - an alkene with a double bond.
- Butane (C₄H₁₀) - an alkane with single bonds.

2. **Understand pKa and Ka**:
- pKa is the negative logarithm of the acid dissociation constant (Ka).
- A lower pKa value indicates a stronger acid (higher Ka), while a higher pKa value indicates a weaker acid (lower Ka).

3. **Analyze Hybridization**:
- 1-butyne has sp hybridized carbon atoms, which have 50% s-character.
- 1-butene has sp² hybridized carbon atoms, which have 33% s-character.
- Butane has sp³ hybridized carbon atoms, which have 25% s-character.

4. **Relate s-character to Acidity**:
- The higher the s-character, the more electronegative the atom, and the stronger the acid. This is because the s-orbital is closer to the nucleus, which stabilizes the negative charge of the conjugate base after deprotonation.
- Therefore, 1-butyne (50% s-character) is more acidic than 1-butene (33% s-character), which is more acidic than butane (25% s-character).

5. **Determine the Order of Acidity**:
- 1-butyne > 1-butene > Butane
- This means that 1-butyne has the lowest pKa, followed by 1-butene, and butane has the highest pKa.

6. **Write the Increasing Order of pKa**:
- Since we need to arrange them in increasing pKa, we have:
- Butane (highest pKa)
- 1-butene (middle pKa)
- 1-butyne (lowest pKa)
- Thus, the increasing order of pKa values is:
- Butane < 1-butene < 1-butyne

### Final Answer:
**Increasing order of pKa values**: Butane < 1-butene < 1-butyne