Conformations of cycloheptadecane. A comparison of methods for conformational searching

As a test of the effectiveness of various methods for searching the conformational space of highly flexible molecules, we conducted a series of conformational searches on cycloheptadecane. The methods studied included systematic and random conformational searches in both internal (torsion angle) and external (Cartesian) coordinate frames. Distance geometry and molecular dynamics were also investigated. While none of the methods examined found all the low-energy conformations in a single search, all methods except distance geometry located the same global minimum. Some methods performed better than others at finding the other low-energy conformers. In all, 262 conformations of cycloheptadecane having MM2 energies within 3 kcal/mol of the global minimum were discovered. Amonghighly symmetrical structures, cycloheptadecane lies close to the boundary distinguishing problems which can and cannot be adequately addressed by using contemporary methodology and resources.