Ketones are less reactive than aldehydes because

Options

A. C = O group is less polar in ketones
B. of electromeric effect
C. steric hindrance to the attacking reagent
D. none of these

Answer

To understand why ketones are less reactive than aldehydes, we can break down the explanation into several key points:

### Step-by-Step Solution:

1. **Understanding the Structures**:
- **Aldehydes** have the general structure R1-CHO, where R1 is an alkyl group and the carbonyl group (C=O) is bonded to a hydrogen atom.
- **Ketones** have the structure R1R2C=O, where R1 and R2 are both alkyl groups.

2. **Reactivity in Nucleophilic Addition**:
- The reactivity of carbonyl compounds in nucleophilic addition reactions is influenced by the electrophilicity of the carbon atom in the carbonyl group. The more electrophilic the carbon, the more reactive the compound.

3. **Steric Hindrance**:
- In ketones, the carbonyl carbon is bonded to two alkyl groups (R1 and R2), which creates steric hindrance. This means that there is more crowding around the carbonyl carbon, making it harder for nucleophiles to approach and attack the carbon.
- In contrast, aldehydes have only one alkyl group and one hydrogen atom, resulting in less steric hindrance. This allows nucleophiles to approach the carbonyl carbon more easily.

4. **Electronic Effects**:
- Alkyl groups exhibit a +I (inductive) effect, which pushes electron density towards the carbonyl carbon. In ketones, the presence of two alkyl groups increases the electron density around the carbonyl carbon, making it less electrophilic.
- Aldehydes, having only one alkyl group, have a lower electron density around the carbonyl carbon, making it more electrophilic and thus more reactive.

5. **Conclusion**:
- The combination of increased steric hindrance and the electronic effects of the alkyl groups leads to the conclusion that ketones are less reactive than aldehydes in nucleophilic addition reactions.

### Final Answer:
Ketones are less reactive than aldehydes primarily due to increased steric hindrance from the two alkyl groups attached to the carbonyl carbon in ketones, which makes it harder for nucleophiles to approach. Additionally, the electron-donating effect of the alkyl groups in ketones reduces the electrophilicity of the carbonyl carbon compared to aldehydes.

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