Conformations of Flexible Calixarenes in Solution

Since the calixarenes form complexes with a variety of guests (see Chapter 5) it is not surprising that their conformational mobility is influenced by cations. 

Conformational mobility of calixarenes with one or more hydroxyls replaced by other groups 

Ring size Lower rim groups Solvent AG kcal moP T, °C Ref 

Typical examples are the p-sulfonatocalixarenes, which become somewhat less mobile in the presence of metal ions such as Na and considerably less mobile in the presence of ammonium ions such as phenyltrimethylammonim.  

The NMR spectra of the oxyanions generated by the action of BuLi on p-allylcalix[4]arene in DM SO suggest that the conformations of the mono- and tetra-anions are cone, while those of the di- and tri-anions are less clear (see ref. 1, pp. 124-126). However, X-ray crystal structures of the monosodium and dilithium salts of 4 , generated by the action of NaH or BuLi on the calixarene followed by treatment with MeOH, show both to be in the cone conformation in the solid state.  

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