This work was conducted to explain and evaluate some of the conflicting data reported in the literature on the 2,4-dinitrophenylhydrazones. Various analytical techniques have been applied to the study of the use of 2,4-dinitrophenylhydrazine as a reagent for carbonyl compounds. It is concluded that the discrepancies found in the literature may be due to the occurrence of geometrical isomerism, polymorphism, mixed-crystal formation, structural rearrangements, or side reactions.IT HAS been shown that the discrepancies in the literature concerning the physical properties of the 2,4-dinitrophenylhydrazones may arise from several sources: geometrical isomerism (8-10, 12, 21, 23, 2-5, 36), polymorphism (3, 13. l.'h 18, 22, 31), formation of mixed crystals (6), rearrangements (/, 5),