NMR parameters and geometries of OHN and ODN hydrogen bonds of pyridine-acid complexes |
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Authors: | Limbach Hans-Heinrich Pietrzak Mariusz Sharif Shasad Tolstoy Peter M Shenderovich Ilya G Smirnov Sergei N Golubev Nikolai S Denisov Gleb S |
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Institution: | Institut für Chemie, Freie Universit?t Berlin, Takustrasse 3, Berlin, Germany. limbach@chemie.fu-berlin.de |
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Abstract: | In this paper, equations are proposed which relate various NMR parameters of OHN hydrogen-bonded pyridine-acid complexes to their bond valences which are in turn correlated with their hydrogen-bond geometries. As the valence bond model is strictly valid only for weak hydrogen bonds appropriate empirical correction factors are proposed which take into account anharmonic zero-point energy vibrations. The correction factors are different for OHN and ODN hydrogen bonds and depend on whether a double or a single well potential is realized in the strong hydrogen-bond regime. One correction factor was determined from the known experimental structure of a very strong OHN hydrogen bond between pentachlorophenol and 4-methylpyridine, determined by the neutron diffraction method. The remaining correction factors which allow one also to describe H/D isotope effects on the NMR parameters and geometries of OHN hydrogen bond were determined by analysing the NMR parameters of the series of protonated and deuterated pyridine- and collidine-acid complexes. The method may be used in the future to establish hydrogen-bond geometries in biologically relevant functional OHN hydrogen bonds. |
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Keywords: | acid–base complexes hydrogen bonds isotope effects NMR parameters |
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