Using the gauge‐including atomic orbitals approach with B3LYP exchange‐correlation functional in combination with the 6‐311++G(2d,2p) basis set, we have calculated the ¹³C chemical shifts [Δσ] and ¹³C¹³C indirect spin‐spin coupling constants [J(C,C)] for the series of isolated planar polyacetylene chains C_2nH_2n+2, from n = 2 up to n = 11. For both cis and trans isomers, infinite polymer values can be estimated from converged chemical shifts in the central unit of each isomer. The theoretical model predicts the chemical shift difference between the cis and trans forms of 10.28 ppm, in very good concordance with experimental result. The ¹J(CC) and ¹J(CC) calculated values are more geometry‐dependent but they exhibit notable regularity typical for such systems as the size of chain is increased. Variations between ¹J(CC) and ¹J(CC) in the central unit of the C₂₂H₂₄ chain are estimated around 11 Hz, independent of isomeric form. It is found for both ¹J(CC) and ¹J(CC) that variations between the cis and trans forms are in the range of 3–4 Hz, indicating also a distinction of the isomeric form. In addition, our results show that the presence of a structural change on these conjugated backbones has marked influence on the chemical shifts. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010