PARAMETER SET FOR THE PREDICTION OF THE C-13-NMR CHEMICAL-SHIFTS OF SP2-HYBRIDIZED AND SP-HYBRIDIZED CARBON-ATOMS IN ORGANIC-COMPOUNDS

A parameter set was compiled for the prediction of the carbon-13 chemical shifts of sp2- and sp-hybridized carbon atoms based on simple linear additivity relationships. Extensive tests were done against 80 115 known chemical shifts. Many of the previously reported parameters are amended and new parameters are added. Statistical measures of the quality of the prediction are given in cases for which a representative set of examples was available. The parameter set together with previously published increments for sp3-hybridized carbon atoms could predict 97% of the 150 000 chemical shifts investigated, with a standard deviation of 5.5 ppm. The additivity rules reported can be used alone or in connection with a recently published computer program for the estimation of carbon-13 chemical shifts. This program automatically selects and applies the additivity rules appropriate to the individual carbon atoms of the chemical constitution entered.