<P> Crystals of different hydrazones have characteristic melting and boiling points, allowing the identity of a substance to be determined in a method known as derivatization . In particular, the use of 2, 4 - dinitrophenylhydrazine was developed by Brady and Elsmie . Modern spectroscopic and spectrometric techniques have superseded these techniques . </P> <P> Dinitrophenylhydrazine does not react with other carbonyl - containing functional groups such as carboxylic acids, amides, and esters, for which there is resonance - associated stability as a lone - pair of electrons interacts with the p orbital of the carbonyl carbon resulting in increased delocalization in the molecule . This stability would be lost by addition of a reagent to the carbonyl group . Hence, these compounds are more resistant to addition reactions . Also, with carboxylic acids, there is the effect of the compound acting as a base, leaving the resulting carboxylate negatively charged and hence no longer vulnerable to nucleophilic attack . </P>

Reaction of aldehyde and ketone with 2 4-dinitrophenylhydrazine