A combined experimental and theoretical study on the conformational behavior of a calix[6] arene

An experimental and theoretical study on the conformational behavior of the 1,3,5-OMe-2,4,6- OCH2CONHOH-p-tert- butylcalix[ 6] arene has been carried out. In particular, semiempirical (AM1) and density functional theory (DFT) calculations have been performed in order to identify the possible conformers. The obtained results show that the cone structure is the most stable conformer at any level of theory, even if significant differences have been obtained for the other species. The inclusion of solvent effect, through a continuum model, also points out the relevant role played by the solvent in the stabilization of the cone structure in solution. These latter results have been confirmed by NMR experiments, which clearly show the presence of only the cone conformer in a polar solvent, such as DMSO. Finally, H-1 and C-13 NMR spectra on model systems, i.e., two successive phenol rings (Ar-1-CH2-Ar-2), have been computed at the DFT level and compared with the experimental spectra of the complete molecule. The results show an overall good agreement with the experimental data, thus leading to an unambiguous assignment of the experimental spectra.