Carbon-13 N.M.R. chemical shift and electronic structure of an infinite polymer chain as studied by tight-binding MO theory Polyethylene, and cis and trans polyacetylenes

Abstract

A tight-binding MO theory has been used to derive a formalism for calculating the ¹³C N.M.R. chemical shift of an infinite polymer chain with the sum-over-state approximation. This formalism has been applied to the calculation of the ¹³C N.M.R. shielding tensor of polyethylene using the extended Hückel MO theory. In order to discuss the specification of the finite interaction length for the ¹³C N.M.R. chemical shift of any specified CH₂ group of polyethylene chain, ¹³C N.M.R. chemical shifts of some n-paraffins with 1–16 carbon atoms are calculated in the sum-over-state approximation using the extended Hückel MO theory, and are compared with the experimental values. In addition the ¹³C N.M.R. chemical shifts of polyacetylenes with trans and cis forms are calculated using the above theory and the results are found to agree with the experimental data.