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

L.C. Groenen, Leo C. Groenen, Erich Steinwender, Bert T.G. Lutz, Joop H. van der Maas, David Reinhoudt

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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.
    Original languageUndefined
    Pages (from-to)1893-1898
    Number of pages5
    JournalJournal of the Chemical Society. Perkin transactions II
    Volume0
    Issue number2
    DOIs
    Publication statusPublished - 1992

    Keywords

    • METIS-106772
    • IR-12591

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