Two series of para disubstituted benzenes were studied: 2-(4-X-phenyl)-1,3-dihydro- 2H-isoindole-1,3-diones (1) and 3-(4-X-phenyl)-3,4-dihydro-2H-1,3-benzoxazine-2,4-diones (2). Their 1H and 13C chemical shifts were correlated with substituent shift increments (SSI) aj and zj, respectively. For 13C chemical shifts, all four zj values, zi, zo, zm, and zp, were used to check the assignment and to find out possible variables for improvement of regression equations. Significant deviations from plain additivity were observed in the case of δH3 and δC3 chemical shifts. This can be explained by changes in diamagnetic anisotropy contribution induced by different twist of 4-substituent from the benzene plane caused by variable substituent in position 1.