Which one of the following compounds will be most readily dehydrated?

Options

A.
B.
C.
D.

Answer

To determine which compound will be most readily dehydrated, we need to analyze the stability of the carbocation formed during the dehydration process. The stability of the carbocation is influenced by the effects of substituents attached to the carbon chain, specifically the +I (inductive) and -I (inductive) effects.

### Step-by-Step Solution:

1. **Identify the Compounds**: We have four compounds, each containing a keto group (C=O) and an adjacent hydroxy group (OH).

2. **Understand Dehydration**: Dehydration involves the removal of the OH group, which leads to the formation of a carbocation. The stability of this carbocation is crucial for determining the ease of dehydration.

3. **Carbocation Formation**: When the OH group is removed, a positive charge is created at the carbon atom where the OH group was attached. This positive charge characterizes the carbocation.

4. **Evaluate Carbocation Stability**: The stability of the carbocation is directly proportional to the +I and +M effects (electron-donating effects) and inversely proportional to the -I and -M effects (electron-withdrawing effects).
- The keto group (C=O) exerts a -I effect, which destabilizes the carbocation.

5. **Distance Dependence**: The effects of substituents are distance-dependent. The closer the -I group is to the carbocation, the greater its destabilizing effect. Conversely, if the -I group is further away, its destabilizing effect is reduced.

6. **Analyze Each Compound**:
- **Option 1**: Carbocation is formed one bond away from the keto group.
- **Option 2**: Similar to option 1, the carbocation is also one bond away from the keto group.
- **Option 3**: The carbocation is formed two bonds away from the keto group, reducing the -I effect's influence.
- **Option 4**: The carbocation is one bond away from the keto group.

7. **Conclusion**: Since the carbocation in option 3 is formed at a distance of two bonds from the keto group, it experiences less destabilization due to the -I effect compared to the other options. Therefore, option 3 will be the most readily dehydrated compound.

### Final Answer:
**Option 3** is the compound that will be most readily dehydrated.