Talk:Calixarene
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Thanks a lot for excellent paper. But there is some unclear information concerning calixarene`s conformational chemistry. It is known that the mobility of calixarene`s framework is important supramolecular characteristic. Some comments.. «The 4 hydroxyl groups interact by hydrogen bonding and stabilize the cone conformation. This conformation is in dynamic equilibrium with the other conformations. Conformations can be locked in place with proper substituents replacing the hydroxyl groups which increase the rotational barrier. Alternatively placing a bulky substituent on the upper rim also locks a conformation.» First of all the calixarene with hydroxyl group have the rigid conformation because of the very strong intramolecular hydrogen bond. Only pinched cone-pinched cone conventional observed. After alkylation of lower rim two different mode of rotation may be possible. (para substituent through the annulus and oxygen through the annulus). For calix[4]arenes there is contradictory information. Referring to (Ikeda A., Shinkai S., Novel Cavity Design Using Calix[n]arene Skeletons: Toward Molecular Recognition and Metal Binding, Chem. Rev. 1997, 97, 1713-1734. (12(3))) Calix[4]arenes have two possible mode of rotation. But referring to.. Jan Lang, Jiri Vlach, Hana Dvorakova, Pavel Lhotak, Michal Himl, Richard Hrabal, Ivan Stibor, Thermal isomerisation of 25,26,27,28-tetrapropoxy-2,8,14,20-tetrathiacalix[4]arene: isolation of all four conformers, Journal of the Chemical Society, Perkin Transactions 2 (Physical Organic Chemistry), 1 (2001), 4 ( 07), 576-580. Calix[4]arenes have only one mode of rotation (oxygen through the annulus). Consequently calix[4]arene (-O-Pr in lower rim) is conformational rigid irrespective of para-substituent referring to Jan Lang. The calix[4]arene is conformational mobile when H is para-substituent reffering to Shinkai S. Haw many inversion for calix[4]arene skelleton are possible for calix[4]arene two or one?
With best regards Vasiliy M. (support the Russian wiki-paper devoted to calixarene).
Metal [1] 13:15, 12 February 2007 (UTC)
