Conformations of Calixarenes in the Solid State

Calix[4]arenes containing four endo-OH groups exist in the cone conformation in the solid state. The first X-ray structure of a calix[4]arene to show this 

A lone exception has been reported describing the isolation of two crystalline forms of p-hexanoylcalix[4]arene which, on the basis of CP-MAS NMR spectral measurements, are assigned cone (one C=0 resonance) and partial cone (3 C=0 resonances) stuctures. 

Fujiwara, T. Tomita, K.-I. Asfari, Z. Vicens. J. J. Inclusion Phenom. Mol. Recognit. Chem. 1993, 15, 341. 

An X-ray structure of the corresponding de-terr-butyl compound 90c (R = showed this compound to also exist in a cone conformation, indicating that the p-substituent has little effect on the solid state conformation of calix[4]arenes. 

Relatively few X-ray structures of calix[4]arenes in the partial cone conformation have been reported (see ref. 1, pp. 106-107), most of them involving tetra-0- 

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