CAVITANDS AS VERSATILE MOLECULAR RECEPTORS

X-ray crystal structure of 3.2PhF and H-1 NMR complexation studies in solution reveal the strong tendency of cavitand 3 to selectively bind aromatic guests in organic solution. The association constants (K(a)) for eight 1:1 caviplexes formed in acetone-d6 were determined. The solvation effect is largely responsible for the relatively low K(a) values observed. The orientation assumed by the guests inside the cavity is determined by dipole-dipole interactions between the host and the guest; additional CH3-pi interactions are present in the case of 3.3(CH3)2CO. The modification of the structure of 3 by introducing a suitable and furtherly modifiable substituent allowed the synsesis of optically pure chiral cavitand 5. H-1 NMR complexation studies of 5 in acetone-d6 reveal that the CH2OH group perching on top of the cavity rim affects the selectivity but not the orientation of the included aromatic guests for the 1:1 caviplexes formed.