Application of semi-empirical calculations of 13C chemical shifts and 1J(CH) coupling constants to the analysis of carbonium ion structures

¹³C chemical shifts and ¹³CH coupling constants for classical and non-classical structures of some typical carbonium ions have been calculated by the method of summation over excited states in the INDO approximation using a special parameterization. Comparison of the data obtained with the experimental values shows that the calculation of the chemical shifts and spin-spin coupling constants is superior to energy calculations, and provides a useful means for the study of the structure of carbonium ions.