PREDICTION OF THE C-13 NMR CHEMICAL-SHIFTS OF POLYSUBSTITUTED BENZENES WITH HOMOGENEOUS SUBSTITUENTS

A new incremental scheme for the calculation of the C-13 NMR chemical shifts in polysubstituted benzenes with homogeneous substituents was derived and applied to spectral prediction for C6X(n)H6-n where X = CH3, C2H5, i-C3H7, CF3, F, Cl, Br, COOH. Owing to the use of only two-particle increments the procedure is simple enough to be carried out on hand calculators, and gives complete agreement with experimental values within a few tenths of a ppm in all cases compared (76 compounds). The C-13 NMR chemical shift was predicted for hexaethylbenzene with a good fit to the experiment value, and also for 20 unmeasured compounds. The present scheme can be used as an algorithm in structure-searching programs for personal computers, and in data-based systems.