Arrange the following compounds in decreasing orders of rate of hydration.
`(X) C Cl_(3)CHO " " (Y) CH_(3)CHO " " (Z)CH_(3)COCH_(3) " " (W) CF_(3)CHO`

Options

A. W > Z > X > Y
B. W > X > Y > Z
C. W > Y > Z > X
D. W > Z > Y > X

Answer

To arrange the compounds (X) CCl₃CHO, (Y) CH₃CHO, (Z) CH₃COCH₃, and (W) CF₃CHO in decreasing order of their rate of hydration, we need to analyze the electrophilicity of the carbonyl carbon in each compound. The more electrophilic the carbonyl carbon, the faster it will react with water (hydration).

### Step-by-Step Solution:

1. **Identify the Compounds**:
- (X) CCl₃CHO
- (Y) CH₃CHO
- (Z) CH₃COCH₃
- (W) CF₃CHO

2. **Understand Electrophilicity**:
- The rate of hydration depends on how electrophilic the carbonyl carbon is. A more electrophilic carbon will attract water molecules more readily.
- Electron-withdrawing groups increase the electrophilicity of the carbonyl carbon by stabilizing the positive charge that develops during the reaction.
- Conversely, electron-donating groups decrease electrophilicity.

3. **Analyze Each Compound**:
- **(W) CF₃CHO**: The CF₃ group is a strong electron-withdrawing group, making the carbonyl carbon highly electrophilic. Thus, it will have the highest rate of hydration.
- **(X) CCl₃CHO**: The CCl₃ group is also an electron-withdrawing group, but not as strong as CF₃. Therefore, it will be less electrophilic than (W) but more than the others.
- **(Y) CH₃CHO**: The CH₃ group is an electron-donating group, which reduces the electrophilicity of the carbonyl carbon compared to (W) and (X).
- **(Z) CH₃COCH₃**: This compound has two CH₃ groups, which are both electron-donating. This makes it the least electrophilic among the four.

4. **Order of Electrophilicity**:
- Based on the analysis, we can arrange the compounds in decreasing order of their rate of hydration:
- (W) CF₃CHO > (X) CCl₃CHO > (Y) CH₃CHO > (Z) CH₃COCH₃

5. **Final Answer**:
- The final order of compounds in decreasing order of rate of hydration is:
- **(W) > (X) > (Y) > (Z)**