The proton chemical shifts and the stereochemical structures of poly(vinyl chloride)

The proton chemical shifts of dyads, triads and tetrads of poly(vinyl chloride) were calculated as a function of racemic unit fraction in a chain by taking account of the diamagnetic contribution, magnetic anisotropy effect and polar effect, based on Pople's approximation. The electron densities on the hydrogen atoms in each of the model compounds for the dyad, triad and tetrad units were calculated by the CNDO/2 method. The statistical weights of the preferred conformations for any specified stereochemical configuration were calculated by generating a set of 100 Monte Carlo chains using Flory's matrix method. Thus the proton chemical shifts of methylene and methyne groups in each of the dyad, triad and tetrad units were calculated by averaging over the preferred conformations. Fairly good agreement between the calculated and the experimental values of the proton chemical shifts for the dyad and triad units were obtained, but some discrepancies were found in the case of tetrads especially mrm tetrads. The dependences of the proton chemical shifts of the dyad, triad and tetrad units upon the racemic unit fraction and on the temperature were discussed.