The twelve novel 4-(substituted-phenyl)-6-methyl-3-phenyl-4H-1,2,4-oxadiazin-5(6H)-one derivatives were synthesized by the reactions of N-Substituted-phenyl-benzamide oximes with 2-bromopropionyl chloride. The synthesized 1,2,4-oxadiazin-5-one derivatives were characterized by their physical constants and IR, (1) H NMR, C-13 NMR and LC/TOF-MS analyses data. The experimental C-13 NMR chemical shifts (ppm) (SSC) of the C=O, C=N, CH and CH3 carbons of these 1,2,4-oxadiazin-5-one derivatives were correlated with the various Hammett substitution constants and Swain-Lupton parameters, using single (SSP) and multi-linear (DSP) regression analysis. Negative rho(I) and rho(R) values were found for correlations of C=O, C=N and CH3 carbons (reverse substituent effect). For the other carbon (CH), positive rho(I) (normal substitution effect) and negative rho(R) (reverse substitution effect) values were calculated by DSP regression analysis. As a result of DSP regression analysis, the C-13 NMR chemical shift of the C= O, C= N and CH carbons of the oxadiazine ring showed a satisfactory correlation (r > 0.90), while excellent correlation was observed at the CH3 carbon (r = 0.99). The C-13 NMR chemical shift values of the C=O, C=N, CH and CH3 carbons of the pi-Br-substituted 1,2,4-oxadiazin-5-one derivative were estimated using the equations obtained by the DSP regression analysis. These predicted C-13 NMR chemical shifts were compared with experimental C-13 NMR chemical shifts for 4-(4-bromophenyl)-6-methyl-3-phenyl-4H-1,2,4-oxadiazine-5(6H)-one derivatives. (C) 2021 Elsevier B.V. All rights reserved.