Parent calixarenes

For the successful characterization of a compound it is generally necessary to obtain it in pure form. Calixarenes, especially when made by one-step procedures, are often produced as a mixture requiring the separation of its components. In some instances, e.g. the one-step syntheses of p-terr-butylcalix[4]-, -[6]-, and -[8]arenes, simple recrystallization suffices. In many other instances, however, chromatographic procedures are necessary, principally flash chromatography and HPLC. The latter, discussed in the previous volume (see ref. 1, pp. 84-85), has been applied to mixtures of the parent calixarenes. The reverse phase HPLC technique is particularly useful for following the separation of the larger members of the family, a typical example of which is shown in Figure... 

For the melting points of the parent calixarenes, see data in Table 3.3. 

Mass spectra (see ref 1, pp. 83-84) continue to be useful in calixarene chemistry, primarily for the determination of the molecular weights of compounds such as the parent calixarenes with n > 8 and numerous other large calixarene-derived compounds e.g. a rigid cavity of nanosize dimensions ). Mass spectral deter-... 

Comparison of conformational barriers, IR stretching frequencies, and conformations of parent calixarenes and their fully and partially etheri-fed derivatives... 

X-Ray crystallographic structures of solid state complexes of several of the parent calixarenes with metal ions have been obtained, early examples including the titanium complexes of 4 and 6 , a complex containing two Eu ... 

Cram has proposed the class name cavitand for synthetic organic host compounds that contain enforced or rigid cavities large enough to accommodate simple molecules or ions (136). The parent calixarenes (Figure 2.53) are not of this class, whereas the rigid modified ones (Figure 2.57)... 

Solid-state inclusion complexes of parent calixarenes with neutral molecules... 

Abstract. The condensation of l,l -bis(chlorocarbonyl)metallocenes and p-/er/-butylcalix[4]arene in toluene leads to novel metallocene calix[4]arenes in which the metallocene subunit bridges the opposite hydroxy groups of the parent calixarene. 

Abstract Several facets of pyridinocalixarene chemistry have been investigated including reaction pathways for their formation from the base-catalyzed alkylation of the parent calixarenes with PicCl-HCl, effect of the nature and identity of the base on regio- and stereoselective O-alkylations, creation of molecular asymmetry in calix[4]arenes and enantiomeric resolution, conformation and conformational mobility, and complexation. 

In solution, the H-NMR spectra of la-MeCN and la-2MeCN did not give separate resonances for included MeCN and free MeCN. Therefore, a rapid equilibrium between included MeCN and free MeCN in solution is expected. Even in the solid state, the included MeCN is only loosely bound in the calixarene cavity and it can be completely removed in vacuo (0.1 mm Hg) in one day. However, the structure is important as a model for the calixarene part of the more complex molecules described below which, though they were often obtained in crystalline form, always failed to diffract sufficiently to allow X-ray structure determination. Instead it is necessary to rely on spectroscopic techniques, comparing the NMR spectra with that of the parent calixarene whose structure is known (Figure 1). 

All of the parent calixarenes with carbon bridges are conformationally flexible in solution [l, 3]. For instance, the cone conformation of calix[4]arene is transformed to its inverted cone conformation in solution at ambient temperature (Scheme 11). 

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