the 13c chemical shifts for a series of compounds which includes carboxylic acids, aldehydes, ethers, ketones and hydrocarbons were simulated by using the parametric techniques. the observed chemical shifts were related to numerically encoded structural parametes called descriptors. two new electronic descriptors were added to the previous descriptors. ploting of experimental versus calculated ...

We give a proper reparametrization theorem for a set of rational parametric equations which is proper for all but one of its parameters. We also give an algorithm to determine whether a set of rational parametric equations belongs to this class, and if it does, we reparametrize it such that the new parametric equations are proper.