Calixarenes intramolecular hydrogen-bonding interactions

Perceiving a similarity between the shape of a Greek vase known as a Calix Crater and the shape of the cyclic tetramer, as illustrated in Fig. 11., we assigned the name calixarene 3,4). If the calixarenes assume the shape designated as the cone conformation (see Sect. 5.1) they are seen to have cavities whose dimensions increase as the number of arene moieties in the maerocyclic array increases, as illustrated in Fig. 12. Whether the shapes of these cavities are time-invariant depends on the flexibility of the calixarene (see Sect. 5.2) whether the open conformation exists depends on intramolecular hydrogen bond interactions. There is evidence (see Sect. 5.1), for example, that the calix[6]arenes and calix[8]arenes exist in solution in nonpolar solvents in transannularly pinched conformations, as illustrated in Fig. 13. x-Ray crystallographic determinations have established that in the solid state the calix[4]-arenes exist in the cone conformation 29,30), the calix[5]arenes in the cone conformation 31,32), and the derivatives of the calix[6]arenes and calix[8]arenes in the alternate rather than cone conformation 33,34). 

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