Abstract The reaction of 1,2‐ethylenediamine with seven fluorinated β‐diketones affords two different 1,4‐diazepine series depending on the experimental conditions. Their structures as well as tautomerism have been established by 1 H, 13 C, 15 N and 19 F nuclear magnetic resonance in solution supported by density functional theory calculations at the B3LYP/6‐311++G(d,p) level. The two compounds obtained from ( E )‐5‐(2‐fluoro‐4‐hydroxyphenyl)‐1‐phenylpent‐4‐ene‐1,3‐dione were analyzed by X‐ray crystallography and studied by solid‐state NMR.