Comparative analysis of 13C shielding constants stereospecificity in the silicon and germanium derivatives of acetylenic aldehyde and ketone oximes based on the 13C NMR spectroscopy and GIAO calculations

• Published in: Magnetic resonance in chemistry 2009-07, Vol.47 (7), p.601-604
• Main Authors: Afonin, Andrei V., Pavlov, Dmitry V., Mareev, Alexander V., Simonenko, Dmitry E., Ushakov, Igor A.
• Format: Article
• Language: English
• Subjects: 13C NMR; GIAO calculations; NMR; shielding constants; silicon and germanium derivatives of acetylenic aldehyde and ketone oximes; stereospecificity
• ISSN: 0749-1581; 1097-458X
• DOI: 10.1002/mrc.2435

In the acetylenic aldehyde oximes with substituents containing silicon and germanium, the 13C NMR signal of the C‐2 carbon of triple bond is shifted by 3.5 ppm to lower frequency and that of the C‐3 carbon is moved by 7 ppm to higher frequency on going from E to Z isomer. A greater low‐frequency effect of 5.5 ppm on the C‐2 carbon signal and a greater high‐frequency effect of 11 ppm on the C‐3 carbon signal are observed in the analogous acetylenic ketone oximes. The carbon chemical shift of the CN bond is larger by 4 ppm in E isomer relative to Z isomer for the aldehyde and ketone oximes. The 29Si chemical shifts in the silicon containing acetylenic aldehyde and ketone oximes are almost the same for the diverse isomers. The trends in changes of the measured chemical shifts are well reproduced by the gauge‐including atomic orbital (GIAO) calculations of the 13C and 29Si shielding constants. Copyright © 2009 John Wiley & Sons, Ltd. The chemical shifts of the C‐2 and C‐3 carbons of triple bond in the acetylenic oximes exhibit a significant difference in the diverse isomers. The C‐2 chemical shift is larger whereas the C‐3 chemical shift is smaller in E isomer relative to Z isomer. The stereospecificity of the 13C shielding constants in the ketoximes is much more pronounced in comparison with the aldoximes.