Conformations of calix[4]arenes-an investigation based on CSD data. Part II. Partial cone, 1,2-alternate and 1,3-alternate conformers of methyleneand heteroatom-bridged calix[4]arenes In the first part of this investigation (Part I), cone conformers of calix[4]arenes with methylene and heteroatom bridges from the Cambridge Structural Database (CSD) were investigated. Previously introduced parameters α, β and δ were utilized in describing the conformations of the hydrocarbon base frame of the above mentined compounds. In this part of the investigation, partial cone, 1,2-and 1,3-alternate conformers of methylene-and heteroatom-bridged calix[4]arenes are studied and the influence of inter-and intramolecular interactions on the conformations of these compounds is evaluated.

Conformations of calix[4]arenes -an investigation based on CSD data. Part I. Cone conformers of methylene-and heteroatom-bridged calix[4]arenesConformations of calix[4]arenes with methylene and heteroatom bridges from the Cambridge Structural Database (CSD) were investigated with the help of the previously introduced parameters α, β and δ. The usefulness of these parameters in describing the conformations of the scaffolds of the above mentioned compounds was demonstrated. The dependence of the values of these parameters on inter-and/or intramolecular interactions present in the structure was investigated in order to discover how the geometry of the calix[4]arene moiety depends on the above listed effects. Structures with C 4v symmetry in the cone group have both β and δ close to 0°. With deformation of the calix[4]arene symmetry towards C 2v (flattened cone structures), the β parameter increases. Deformation towards C s symmetry is best reflected by increase of the parameter δ. Parameter α reflects the degree of 'opening' of the calix[4]arene cavity; structures with four OH groups at the lower rim tend to have lower α and therefore more open structure.

Variation of the stereoparameters for description geometry of calix[4]arenes-more suitable solution for «flat systems» This article deals with a variation of previously introduced parameters α, β, and δ which were used to describing the all possible conformations of these compounds, cone, partial cone, 1,2-and 1,3-alternate conformers of methylene-and heteroatom-bridged calix[4]arenes. Usefulness of these parameters α, β, δ have been already demonstrated, but, it seems, to be more suitable to do any variations them for flat systems. The background for the parameters α, β, δ lies in the representation of the scale of the angles of the calix[4]arene rings towards the reference plane. The original scale 0°-360° for these angles depicts very well the differences between the calix[4]arene conformations but has two significant disadvantages. The first one is the discontinuity of the scale. The angles α i range approximately from 0° to 110° and from 250° to 360° because of the sterical hindrance that would occur should the calixarene phenyl ring enter the cavity. The second disadvantage is the discontinuity at the point α i = 0°, it means the case of flat systems. These flat systems are usually the 'transitions states' between the calixarene conformations and cannot be observed using parameters α, β, δ. To eliminate the difficulties in describing the 'transition states' between the calix[4]arene conformations caused by the discontinuities of the original scale, the new scale should be introduced. New parameters α´, β´, δ´ were introduced by subtracting 360° for each 'negative' ring present in the structure (one for partial cone conformers, two for 1,2-and 1,3-alternate conformers); after the parameters α, β, δ are calculated.

Conformations of Calix[4]arenes. An Investigation Based on CSD Data. Part III. Calix[4]resorcinarenes In the first part of this investigation (Part I), cone conformers of calix[4]arenes with methylene and heteroatom bridges from the Cambridge Structural Database (CSD) were investigated, in the second part (Part II) we focused on structures of partial cone, 1,2-alternate and 1,3-alternate conformers with methylene-and heteroatom-bridged calix[4]arenes represented in this Part II. This, third part (Part III) of the review is a sequel and it is on conformations and geometry of calix[4]resorcinarenes scafolds, again using the data from the CSD. The results were compared to data of calix[4]arene structures in our previous work. The effects of substitutions and inter/intramolecular interactions present in the structure on the symmetry of the resorcinarene base frame were evaluated with the help of previously introduced stereochemical parameters α, β, and δ. Utilization of new, slightly modified scale of parameters α', β', δ' was tested, too. To sum up, these parameter are useful not only for describing the geometry of calix[4]arenes, but for calix[4]resorcinarenes, too. The calix[4]resorcinarenes seem to be more conformationally flexible and the «flat» arrangements are more favoured there. Generally, the substitution is more complex and more irregular in the case of calix[4]resorcinarenes, and it is relatively difficult to found some common patterns. However, as all these results were obtained from solid state data, no conclusion concerning conformations and behavior of these molecules in solution can be stated, similary as in the case of calix[4]arenes.