IR and NMR spectra,intramolecular hydrogen bonding and conformations of para-tert-butyl-aminothiacalix[4]arene in solid state and chloroform solution |
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Authors: | Elena E Zvereva Sergey A Katsyuba Alexander E Vandyukov Alla V Chernova Valery I Kovalenko Svetlana E Solovieva Igor S Antipin Alexander I Konovalov |
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Institution: | 1. A.E.Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Centre of the Russian Academy of Sciences, Arbuzov str. 8, 420088 Kazan, Russia;2. Kazan State University, Kremlevskaja str. 18, 420008 Kazan, Russia |
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Abstract: | It is demonstrated that dissolution of aminothiacalix4]arene in chloroform results in transformation of 1,3-alternate conformation, adopted in single-crystal and bulk polycrystalline solids, to the pinched-cone form. This conformer is stabilised by the intramolecular hydrogen bonds of two distal amino-groups acting as H-donors with another two amino moieties that appear as H-acceptors. The H-bonds cause quite small (ca. 10–20 cm?1) red shift of the IR bands of the NH2 stretching vibrations, which suggests rather weak NH?N hydrogen bonding. This latter is sufficient to stabilize the pinched-cone conformation in the chloroform solution, but the energy gap between the pinched-cone and other conformations is small, and solid-state intermolecular forces easily overcome it, leading to realisation of the 1,3-alternate conformer. The comparison of the DFT computed and experimental vibrational and NMR spectra demonstrates good quality of present quantum-chemical computations, allows complete interpretation of the spectra and reveals simple IR and NMR spectroscopic markers of the conformers of aminothiacalix4]arenes. |
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