2,4-Dinitrophenylhydrazon v. 1-Hydroxy-4-formyl-buten-(3);trans-5-Hydroxy-penten-2-al-2,4-dinitro-phenylhydrazon;5-hydroxy-pent-2-enal-(2,4-dinitro-phenylhydrazone);5-Hydroxy-pent-2-enal-(2,4-dinitro-phenylhydrazon);5-[(2,4-Dinitrophenyl)hydrazinylidene]pent-3-en-1-ol