Theoretical Studies on the Structures and Strain Energies of Cycloparaphenylenes

The structures and strain energies of cycloparaphenylenes (CPPs) have been determined by DFT calculation at the B3LYP/6-31G(d) level of theory. Fifteen stable conformations of 12CPP were found as local minimum structures. It was also found that benzene rings of 12CPP can rotate rather freely at room temperature. The strain energies of nCPP (n = 6-20) were estimated on the basis of the homodesmotic reaction using CPP, biphenyl, and p-terphenyl. It was also found that CPPs have higher strain energy in comparison to cycloparaphenyleneacetylenes (CPPAs).