Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to steric and electronic reasons.
Sterically, the presence of two relatively large substituents in ketones hinders the approach of nucleophile to carbonyl carbon that in aldehydes having only one such substituent.
Electronically, two alkyl groups reduce the electrophilicity of the carbonyl carbon more effectively in ketones than in aldehyde.
Hence, Aldehydes are more reactive towards nucleophilic addition reactions than Ketone.

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**Introduction:**
Aldehydes and ketones are both carbonyl compounds that contain a carbon-oxygen double bond. However, aldehydes are generally more reactive than ketones. This difference in reactivity can be attributed to several factors, including the nature of the carbonyl group, the presence of an alpha hydrogen, and the steric hindrance.

**1. Nature of the carbonyl group:**
The reactivity of aldehydes and ketones is influenced by the nature of the carbonyl group. In aldehydes, the carbonyl carbon is bonded to one hydrogen atom and one alkyl or aryl group. This makes the carbonyl carbon more electrophilic compared to ketones, where the carbonyl carbon is bonded to two alkyl or aryl groups. The presence of the more electronegative hydrogen atom in aldehydes enhances the electrophilicity of the carbonyl carbon.

**2. Presence of alpha hydrogen:**
Aldehydes have an alpha hydrogen atom directly attached to the carbonyl carbon, whereas ketones lack this hydrogen. The presence of the alpha hydrogen in aldehydes makes them more acidic compared to ketones. This acidity allows aldehydes to undergo various reactions, such as aldol condensation, Cannizzaro reaction, and nucleophilic addition reactions, which are not observed in ketones.

**3. Steric hindrance:**
Steric hindrance refers to the obstruction of the reaction due to bulky substituents near the reaction site. Ketones generally have two alkyl or aryl groups attached to the carbonyl carbon, which leads to more steric hindrance compared to aldehydes that have only one alkyl or aryl group. This steric hindrance in ketones makes it difficult for nucleophiles to approach the carbonyl carbon, resulting in lower reactivity compared to aldehydes.

**Conclusion:**
In conclusion, aldehydes are more reactive than ketones due to the presence of an alpha hydrogen, the nature of the carbonyl group, and the reduced steric hindrance. These factors enhance the electrophilicity of the carbonyl carbon, increase the acidity of aldehydes, and facilitate nucleophilic attack. Understanding the differences in reactivity between aldehydes and ketones is crucial in organic chemistry as it helps predict and explain the outcomes of various reactions involving these functional groups.