In this paper, we discuss the structure of the benzoyl hydrazone of the ethyl ether of 5.5-dimethyl-2,4-dioxohexanoic acid. A mixture of hydrazone and 5-hydroxypyrazoline forms is potentially possible for it, which makes it possible to identify the relationship between the position of the ring-chain equilibrium. It is safe to say that the resulting compound is a product of condensation over the carbonyl group adjacent to the ester group, which was established earlier. An attack on an alternative carbonyl group is not allowed by the large effective volume of the neighboring tert-butyl radical. When studying the IR spectrum of the H2L compound in a pressed KBr tablet, a number of bands are observed in the region of valence oscillations of multiple bonds, including an absorption of about 1740 cm-1 (Fig. 1). This means that the resulting H2L compound in the solid state has a linear hydrazone (AE) structure and the nucleophile condensation follows the carbonyl of the ester group.