Theoretical prediction of ¹³C NMR chemical shifts of polymers using oligomeric approach

Abstract

Combined density functional theoretical (DFT) and ab initio methods have been used for the calculation of ¹³C NMR chemical shifts of some hydrogen-terminated oligomers of ethylene, propylene, isobutylene, ethylene oxide, vinyl alcohol, and acrylonitrile. The ¹³C isotropic chemical shift (δ_iso) values are calculated with respect to theoretical isotropic shielding constant (σ_iso) value of the tetramethylsilane (TMS). The average unsigned error in δ_iso values of the various oligomers varies between 2 and 5 ppm. The error of ca. 5.22 ppm for acrylonitrile arises mainly due to the cyano carbon. Oligomeric approach has been employed to calculate the δ_iso values of the corresponding polymers. This approach is validated by the excellent correlation obtained for the linear fits. These calculated δ_iso values for the polymers are in good agreement with the experimental values.