CONE - PARTIAL-CONE ISOMERISM IN TETRAMETHOXYCALIX[4]ARENES - INFLUENCE OF SOLVENT POLARITY AND METAL-IONS

It was found that the ''cone'' - ''partial-cone'' equilibrium in 25,26,27,28-tetramethoxycalix[4]arene derivatives is sensitively affected by the solvent polarity: the cone% increases with the increase in the solvent polarity. The novel finding was rationalized in terms of the difference in the dipole moment: cone conformers with four dipole moments orientating into the same direction are more polar than partial-cone conformers with one inverted phenyl unit and therefore are more stabilized in polar solvents. Alkali metal cations such as Li+ and Na+ strongly interact with four methoxy oxygens, resulting in the shift of the equilibrium to cone.