COMPUTATIONAL STUDIES OF CALIX[4]ARENE HOMOLOGS - INFLUENCE OF 5,11,17,23-SUBSTITUENTS AND 25,26,27,28-SUBSTITUENTS ON THE RELATIVE STABILITY OF 4 CONFORMERS

The effects of 5,11,17,23- and 25,26,27,28-substitutents on the relati ve stability of four conformers of calix[4]arene are discussed on the basis of a computational method using molecular mechanics (MM3) calcul ations. It is shown that a substituent in the lower rim site has a dec isive role in the determination of the stability order among four conf ormers of calix[4]arene, while a substituent in the upper rim site onl y slightly affects the energy differences. It is also shown that in [1 (4)]metacyclophanes with no substituent in the lower rim the structure of 1,2-alternate conformers is very different from the typical 1,2-al ternate structure common to calix[4]arenes.