THE INCREMENT SCHEME FOR THE PREDICTION OF C-13 NMR CHEMICAL-SHIFTS IN POLYCHLORINATED DIBENZO-P-DIOXINS

A topological method for the calculation of C-13 NMR chemical shifts w as developed for polychlorinated dibenzo-p-dioxins (PCDD). Based on pr evious results for polychlorinated benzenes and polyhydroxybenzenes, t he collective influence of the substituents on carbon chemical shifts is presented as the sum of two-particle increments. The increments onl y of two new monosubstituted graphs have to be added to those known fo r PCDD spectra: 1-Cl-DD and 2-Cl-DD. All structural situations in the C-13 NMR chemical shifts of the whole class of 75 PCDD can be covered with a few model compounds. The coefficients of the increment scheme a re independent of the change of CDCl3 for acetone-d(6), so it may be a new reliable criterion for recognizing PCDD by C-13 NMR, in spite of the close resemblance of NMR spectra of aromatic compounds.