Conformational analysis of crown ethers—part 2. 15-crown-5

Abstract

An extensive conformational search of 15-crown-5 was performed with the MM3 force field yielding 3623 conformers ranging in steric energy from 21.40 to 56.24 kcal mol −1. Free energies and conformer population are reported for the gas phase. A continuum dielectric model is used to estimate the conformer populations in a variety of solvents. The three conformers observed in crystal structures containing 15-crown-5 molecules that do not form inner sphere complexes with metal ions are predicted to be among the most populated conformations in condensed phases. Comparison of the structural features of the crystallographically observed conformers with those of the energy minimized MM3 structures demonstrates that the MM3 force field well reproduces that experimentally observed structural features. Predicted conformer populations are consistent with 13C NMR and vibrational spectra.