Solvent effects on the conformations and hydrogen bond structure of partially methylated p-tert-butylcalix[4]arenes

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Groenen, Leo C. and Steinwender, Erich and Lutz, Bert T.G. and Maas van der, Joop H. and Reinhoudt, David N. (1992) Solvent effects on the conformations and hydrogen bond structure of partially methylated p-tert-butylcalix[4]arenes. Journal of the Chemical Society. Perkin transactions II, 1992 (2). pp. 1893-1898. ISSN 0300-9580

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Abstract:The effect of the solvent on the conformations of unsubstituted p-tert-butylcalix[4]arene (1) and its methyl ethers 2–6 has been investigated by 1H NMR spectroscopy. The conformational distribution of the 1,2-dimethyl ether 4 and of the tetramethyl ether 6 is strongly influenced by the solvent used. The exact geometry of the cone conformation of the 1,3-dimethyl ether 3 and of the 1,2-dimethyl ether 4 changes from distinct C2 symmetry in CCl4 to close to C4 symmetry in CS2. It seems that inclusion of a small solvent molecule (e.g. CS2) in the cone conformation can take place. Spectra recorded at temperatures up to 125°C in CDCl2CDCl2 showed that the mono- and 1,3-di-methyl ethers are fixed in the cone conformation, whereas the unsubstituted calix[4]arene and the tetramethyl ether are flexible. These observations support a concerted mechanism for the cone-to-cone interconversion in 1, in which two or more phenol rings rotate simultaneously.The hydrogen bonding in partially methylated calix[4]arenes was investigated by IR spectroscopy. In all calix[4]arenes with neighbouring hydroxy groups, a strong cooperativity effect of 80% or more was observed. The exact geometry of the cone conformation affects the strength of the hydrogen bonds, because it influences the O–H O angle in the calix[4]arene. The effect of the solvent on the geometry of the cone conformation is translated in differences of up to 79 cm–1 in the OH-stretch frequencies for spectra recorded in CCl4 and in CS2.
Item Type:Article
Copyright:© 1992 Royal Society of Chemistry
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Link to this item:http://purl.utwente.nl/publications/12591
Official URL:http://dx.doi.org/10.1039/P29920001893
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