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CH···N and CH···O intramolecular hydrogen bonding effects in the 1H, 13C and 15 N NMR spectra of the configurational isomers of 1-vinylpyrrole-2-carbaldehyde oxime substantiated by DFT calculations

✍ Scribed by Andrei V. Afonin; Igor A. Ushakov; Alexander V. Vashchenko; Dmitry E. Simonenko; Andrei V. Ivanov; Alexander M. Vasil'tsov; Al'bina I. Mikhaleva; Boris A. Trofimov

Publisher
John Wiley and Sons
Year
2009
Tongue
English
Weight
167 KB
Volume
47
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

According to the ^1^H, ^13^C and ^15^N NMR spectroscopic data and DFT calculations, the E‐isomer of 1‐vinylpyrrole‐2‐carbaldehyde adopts preferable conformation with the anti‐orientation of the vinyl group relative to the carbaldehyde oxime group and with the syn‐arrangement of the carbaldehyde oxime group with reference to the pyrrole ring. This conformation is stabilized by the CH···N intramolecular hydrogen bond between the α‐hydrogen of the vinyl group and the oxime group nitrogen, which causes a pronounced high‐frequency shift of the α‐hydrogen signal in ^1^H NMR (∼0.5 ppm) and an increase in the corresponding one‐bond ^13^C–^1^H coupling constant (ca 4 Hz). In the Z‐isomer, the carbaldehyde oxime group turns to the anti‐position with respect to the pyrrole ring. The CH···O intramolecular hydrogen bond between the H‐3 hydrogen of the pyrrole ring and the oxime group oxygen is realized in this case. Due to such hydrogen bonding, the H‐3 hydrogen resonance is shifted to a higher frequency by about 1 ppm and the one‐bond ^13^C–^1^H coupling constant for this proton increases by ∼5 Hz. Copyright © 2008 John Wiley & Sons, Ltd.

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