Which one is the correct order of acidity?

Options

A. `CH_2 = CH_2 gt CH_3 - CH = CH_2 gt CH_3 - C -= CH gt CH -= CH`
B. `CH -= CH gt CH_3 - C = CH gt CH_2 = CH_2 gt CH_3 - CH_3`
C. `CH -= CH gt CH_2 gt CH_2 gt CH_3 - C -= CH gt CH_3 - CH_3`
D. `CH_3 - CH_3 gt CH_2 = CH_2 gt CH_3 - C -= CH gt CH -= CH`

Answer

To determine the correct order of acidity among alkanes, alkenes, and alkynes, we can follow these steps:

### Step 1: Understand the relationship between s-character and acidity
The acidity of hydrocarbons is influenced by the s-character of the hybridized orbitals. The more s-character an orbital has, the more acidic the compound tends to be. The order of s-character is:
- sp (50% s-character) > sp2 (33% s-character) > sp3 (25% s-character)

### Step 2: Identify the hybridization of the compounds
Let's analyze the compounds given in the options:
1. **Ethane (C2H6)**: Both carbons are sp3 hybridized.
2. **Propene (C3H6)**: One carbon is sp3 and the other two are sp2 hybridized.
3. **Propyne (C3H4)**: One carbon is sp and the other two are sp2 hybridized.
4. **Ethyne (C2H2)**: Both carbons are sp hybridized.

### Step 3: Compare the acidity based on s-character
Based on the hybridization:
- Ethyne (sp) has the highest acidity due to the highest s-character.
- Propyne (one sp and two sp2) has the next highest acidity.
- Propene (one sp3 and two sp2) follows.
- Ethane (sp3) has the lowest acidity.

### Step 4: Determine the correct order of acidity
From the analysis, the order of acidity from highest to lowest is:
1. Ethyne (most acidic)
2. Propyne
3. Propene
4. Ethane (least acidic)

### Conclusion
The correct order of acidity is:
**Ethyne > Propyne > Propene > Ethane**