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Pronounced stereospecificity of 1H, 13C, 15N and 77Se shielding constants in the selenophenyl oximes as shown by NMR spectroscopy and GIAO calculations
Authors:Andrei V. Afonin  Dmitry V. Pavlov  Igor A. Ushakov  Elena Yu. Schmidt  Al'bina I. Mikhaleva
Affiliation:Irkutsk Institute of Chemistry, 664033 Irkutsk, Russia
Abstract:In the 1H and 13C NMR spectra of 1‐(2‐selenophenyl)‐1‐alkanone oximes, the 1H, the 13C‐3 and 13C‐5 signals of the selenophene ring are shifted by 0.1–0.4, 2.5–3.0 and 5.5–6.0 ppm, respectively, to higher frequencies, whereas those of the 13C‐1, 13C‐2 and 13C‐4 carbons are shifted by 4–5, ~11 and ~1.7 ppm to lower frequencies on going from the E to Z isomer. The 15N chemical shift of the oximic nitrogen is larger by 13–16 ppm in the E isomer relative to the Z isomer. An extraordinarily large difference (above 90 ppm) between the 77Se resonance positions is revealed in the studied oxime isomers, the 77Se peak being shifted to higher frequencies in the Z isomer. The trends in the changes of the measured chemical shifts are well reproduced by the GIAO calculations of the 1H, 13C, 15N and 77Se shielding constants in the energy‐favorable conformation with the syn orientation of the? C?N? O? H group relative to the selenophene ring. Copyright © 2009 John Wiley & Sons, Ltd.
Keywords:NMR  13C NMR  shielding constants  stereospecificity  GIAO calculations  1‐(2‐selenophenyl)‐1‐alkanone oximes
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