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.
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.
Afonin
Andrei V
AV
Irkutsk Institute of Chemistry, 664033 Irkutsk, Russia.
Pavlov
Dmitry V
DV
Ushakov
Igor A
IA
Schmidt
Elena Yu
EY
Mikhaleva
Al'bina I
AI
D002247:Carbon Isotopes; D009682:Magnetic Resonance Spectroscopy / Q000379:methods / Q000592:standards*; D015394:Molecular Structure; D009587:Nitrogen Isotopes; D016566:Organoselenium Compounds / Q000737:chemistry*; D010091:Oximes / Q000737:chemistry*; D011522:Protons; D012015:Reference Standards; D012643:Selenium / Q000737:chemistry*; D013237:Stereoisomerism
D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D016566:Organoselenium Compounds; D010091:Oximes; D011522:Protons; D012643:Selenium