Pronounced stereospecificity of (1)H, (13)C, (15)N and (77)Se shielding constants in the selenophenyl oximes as shown by NMR spectroscopy and GIAO calculations

• Published in: Magnetic resonance in chemistry 2009-10, Vol.47 (10), p.879-884
• Main Authors: Afonin, Andrei V, Pavlov, Dmitry V, Ushakov, Igor A, Schmidt, Elena Yu, Mikhaleva, Al'bina I
• Format: Article
• Language: English
• Subjects: Carbon Isotopes; Magnetic Resonance Spectroscopy - methods; Magnetic Resonance Spectroscopy - standards; Molecular Structure; Nitrogen Isotopes; Organoselenium Compounds - chemistry; Oximes - chemistry; Protons; Reference Standards; Selenium - chemistry; Stereoisomerism
• ISSN: 1097-458X
• DOI: 10.1002/mrc.2471

In the (1)H and (13)C NMR spectra of 1-(2-selenophenyl)-1-alkanone oximes, the (1)H, the (13)C-3 and (13)C-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 (13)C-1, (13)C-2 and (13)C-4 carbons are shifted by 4-5, approximately 11 and approximately 1.7 ppm to lower frequencies on going from the E to Z isomer. The (15)N 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 (77)Se resonance positions is revealed in the studied oxime isomers, the (77)Se 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 (1)H, (13)C, (15)N and (77)Se shielding constants in the energy-favorable conformation with the syn orientation of the-C=N-O-H group relative to the selenophene ring.