Azacalix pyridines, formation

It should be noted that detailed conformational structures of larger azacalix[n] aromatics (n > 4) in solution still remain unknown. For example, the single sets of resonance signals are recorded in NMR spectra for azacalix[n]pyridines (n = 5—10) and azacalix[n]arenes (n = 5—8). The outcomes can probably only suggest the formation of a mixture of conformers which are able to undergo very rapid interconversions at the probe temperature in relative to NMR time scale. Further studies, especially, new strategy and physical methods, are needed to solve the problem. 

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