In this study, two oxazol-5-one derivatives, C20H20N2O2 (1) and C21H22N2O2 (2), were synthesized by getting condensed p-N,N-diethylaminobenzaldehyde with two presented hippuric acid derivatives and in further studies they were analysed spectrochemically. Molecular and crystal structures of the compounds were determined by single-crystal X-ray diffraction and the results revealed that the molecular packing of the crystal structures were stabilized by weak intraand intermolecular interactions also with C-O∙∙∙π, C-H∙∙∙π and π∙∙∙π stacking interactions. Computational studies were also performed using DFT method at B3LYP/6-311G(d,p) level of theory. Vibrational modes and chemical shifts were calculated and compared with the experimental data. In addition, frontier molecular orbitals and molecular electrostatic potential surfaces were simulated. The calculated results show that the optimized geometries can well reproduce the crystal structure. Purpose of this study was to survey the effects of the reactants, which were condensed with each other to produce oxazol-5-one, upon the characteristic properties and crystal forms of the final oxazol-5-one.