Conformational aspects of a "very simple" chain: polyacetylene

Potential energy calcns. of the isolated chains of trans- [25768-71-2] and cis-polyacetylene [25768-70-1] were made to obtain information on the most probable conformations. Previously reported different sets of van der Waals potential functions, different values for the of barrier height to bond rotation, and different geometries for the repeating unit were used. Calcns. were also made of the 7-atom chains of polyacetylene for which independent rotations were allowed around three consecutive quasi-single bonds. The deepest min. on the potential energy map of the trans 3-atom chain were consistent with the all-trans conformation (the most stable one) and with a distorted cis conformation, which deviated from planarity because of the repulsion between H atoms 1 and 4. The energy maps of the cis polymer showed two min., both of which corresponded to nonplanar conformations. From the 7-atom chain anal. of both polymers, in addn. to stable conformations obtained for the 3-atom chains, other min. corresponded to triplets formed from both conformers.