Ring inversion pathways of exo- and endo-calix[4]arenes studied by means of the MM3 force field

Abstract The ring inversion pathways of an exo-calix[4]arene 1a and of p-tert-butylcalix[4]arene 2a were investigated by means of the dihedral driver option of the MM3(92) force field. The calculated activation energies of 14.0 and 6.7 kcal mol−1 are in excellent agreement with the experimentally determined value for p-tert-butylcalix[4]arene and the observed flexibility of the exo-calix[4]arene on the NMR timescale.