The Zincke form of this class of compounds results from the reaction of a pyridinium salt with 2,4-DNP and a primary amine. The presence of this functional group can be distinguished by an absorption 
The Zincke form of this class of compounds results from the reaction of a pyridinium salt with 2,4-DNP and a primary amine. The presence of this functional group can be distinguished by an absorption band around 2720 to 2820 inverse centimeters in IR spectroscopy, or by a chemical shift of around 9-10 delta in proton NMR spectroscopy.  They undergo disproportionation in the Cannizzaro Reaction to yield acids and alcohols, and they can be detected by a brick red precipitate in Fehling's Test or by the formation of a silver mirror on the wall of a test tube in the Tollens test. FTP, name this class of organic compounds defined by a terminal carbonyl group.
The Zincke form of this class of compounds results from the reaction of a pyridinium salt with 2,4-DNP and a primary amine.
aldehydes