Study of stereospecificity of 1 H, 13 C, 15 N and 77 Se shielding constants in the configurational isomers of the selenophene‐2‐carbaldehyde azine by NMR spectroscopy and MP2‐GIAO calculations

In the 1 H and 13 C NMR spectra of selenophene‐2‐carbaldehyde azine, the 1 H‐5, 13 C‐3 and 13 C‐5 signals of the selenophene ring are shifted to higher frequencies, whereas those of the 1 H‐1, 13 C‐1, 13 C‐2 and 13 C‐4 are shifted to lower frequencies on going from the EE to ZZ isomer or from the E moiety to the Z moiety of EZ isomer. The 15 N chemical shift is significantly larger in the EE isomer relative to the ZZ isomer and in the E moiety relative to the Z moiety of EZ isomer. A very pronounced difference (60–65 mg/g) between the 77 Se resonance positions is revealed in the studied azine isomers, the 77 Se peak being shifted to higher frequencies in the ZZ isomer and in the Z moiety of EZ isomer. The trends in the changes of the measured chemical shifts are reasonably reproduced by the GIAO calculations at the MP2 level of the 1 H, 13  C, 15  N and 77 Se shielding constants in the energy‐favorable conformation with the syn orientation of both selenophene rings relative to the C = N groups. The NBO analysis suggests that such an arrangement of the selenophene rings may take place because of a higher energy of some intramolecular interactions. Copyright © 2011 John Wiley & Sons, Ltd.