Intramolecular co-operative hydrogen bond in calix[<Emphasis Type="Italic">n</Emphasis>]arenes (<Emphasis Type="Italic">n</Emphasis> = 4, 6, 8) bearing bulky substituents |
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Authors: | V I Kovalenko L I Maklakov E I Borisoglebskaya L I Potapova E A Shokova I M Vatsouro V V Kovalev |
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Institution: | (1) A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Research Center, Russian Academy of Sciences, 8 ul. Akad. Arbuzova, 420088 Kazan, Russian Federation;(2) Kazan State University of Architecture and Construction, 1 ul. Zelyonaya, 420043 Kazan, Russian Federation;(3) Department of Chemistry, M. V. Lomonosov Moscow State University, 1 Leninskie Gory, 119992 Moscow, Russian Federation |
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Abstract: | Based on the Fourier transform IR spectroscopy together with the published NMR and X-ray data, it was shown that cyclic co-operative
intramolecular hydrogen bond in calixn]arene (n = 4, 6, 8) molecules is mainly responsible for their conformational state irrespective of the presence or absence of bulky
substituents at the upper rim of the molecules. In accordance with the size of a macrocycle (n = 4, 6, 8), the stable conformation, secured by such a hydrogen bond, constitutes a cone, a pinched cone, and a pleated loop, respectively. The new, potentially competing system of hydrogen bonds in calix6]arenes with 3-carboxymethyl-1-adamantyl
substituents does not affect the conformational state of the macrocycle and its H-bonding. Six carboxy groups at the upper
rim form in pairs three cyclic dimers, which does not disturb the hydrogen bonds of the hydroxy groups and the conformation
of the macrocycle. In addition, the cavity of the molecule is considerably enlarged. The removal or rearrangement of the guest
molecules in the solid calixarene by heating up to 180 °C only slightly affects the conformational state of macrocycles bearing
bulky substituents, whereas in calixarenes devoid of such substituents, the similar procedure leads to somewhat of a distortion
of the macrocycles (judging from the IR spectral indications of hydrogen bonding).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1062–1068, June, 2007. |
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Keywords: | calix[n]arenes Fourier transform IR spectroscopy hydrogen bond conformers |
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