Arrange the following in the increasing order of expected enol content.
i. `CH_(3)COCH_(2)CHO`
ii. `CH_(3)COCH_(3)`
iii. `CH_(3)CHO`
iv. `CH_(3)COCH_(2)COCH_(3)`

Options

A. `iii lt ii lt iv`
B. `iii lt ii lt i lt iv`
C. `i lt iv lt ii lt iii`
D. `iv lt i lt ii lt iii`

Explanation

To determine the increasing order of expected enol content for the given compounds, we need to analyze each compound based on the number of alpha-hydrogens and the stability of the enol form. Enol content is generally higher for compounds that can stabilize the enol form through resonance or have more alpha-hydrogens available for tautomerization.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- i. `CH₃COCH₂CHO` (Compound A)
- ii. `CH₃COCH₃` (Compound B)
- iii. `CH₃CHO` (Compound C)
- iv. `CH₃COCH₂COCH₃` (Compound D)

2. **Count the Alpha-Hydrogens**:
- **Compound A (`CH₃COCH₂CHO`)**:
- The alpha-carbon (the carbon adjacent to the carbonyl) is `CH₂`, which has 2 alpha-hydrogens.
- **Compound B (`CH₃COCH₃`)**:
- The alpha-carbon is `CH₃`, which has 3 alpha-hydrogens.
- **Compound C (`CH₃CHO`)**:
- The alpha-carbon is `CH₃`, which has 3 alpha-hydrogens.
- **Compound D (`CH₃COCH₂COCH₃`)**:
- The alpha-carbons are `CH₂` and `CH₃`, which totals to 5 alpha-hydrogens (2 from `CH₂` and 3 from `CH₃`).

3. **Analyze Enol Stability**:
- Enol content is influenced by the stability of the enol form. More alpha-hydrogens generally lead to higher enol content.
- **Compound A**: Can form an enol, but less stable due to fewer alpha-hydrogens.
- **Compound B**: Moderate enol content due to 3 alpha-hydrogens.
- **Compound C**: Similar to Compound B, also has 3 alpha-hydrogens.
- **Compound D**: Highest enol content due to 5 alpha-hydrogens and potential for resonance stabilization.

4. **Arrange in Increasing Order of Enol Content**:
- **Least Enol Content**: Compound A (2 alpha-hydrogens)
- **Next**: Compound B and Compound C (3 alpha-hydrogens each)
- **Most Enol Content**: Compound D (5 alpha-hydrogens)

### Final Order:
1. `CH₃COCH₂CHO` (Compound A)
2. `CH₃COCH₃` (Compound B)
3. `CH₃CHO` (Compound C)
4. `CH₃COCH₂COCH₃` (Compound D)

### Increasing Order of Expected Enol Content:
`CH₃COCH₂CHO < CH₃COCH₃ = CH₃CHO < CH₃COCH₂COCH₃`

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