The aldehydes and ketones undergo many nucleophilic reactions. Aldehydes are generally more reactive than Ketones in nucleophilic addition reactions due to steric and electronic reasons. The aldehydes and ketones undergo a number of reactions due to acidic nature of α-Hydrogen also. Aldol and cross aldol reactions occur in carbonyl compounds which contain α-Hydrogen. Aldehydes and ketones having at least one α-Hydrogen undergo reaction in dil. alkali to form β-hydroxy aldehyde or β-hydroxy ketone. This is aldol reaction. Aldol or ketol lose water to form α,β unsaturated carbonyl compounds which is called aldol condensation. Carbonyl compounds react with ammonia derivatives such as NH₂OH, NH₂NHCONH₂, 2,4 DNP to give products useful in their identification.

Identify the reagent which is used to check the presence of an aldehyde or a keto group in an organic compound.

2,4-dinitrophenylhydrazine is used as a reagent to check the presence of an aldehyde or a keto group in an organic compound.