title: C-H...N and C-H...O intramolecular hydrogen bonding effects in the 1H, 13C and 15N NMR spectra of the configurational isomers of 1-vinylpyrrole-2-carbaldehyde oxime substantiated by DFT calculations.
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 alpha-hydrogen of the vinyl group and the oxime group nitrogen, which causes a pronounced high-frequency shift of the alpha-hydrogen signal in (1)H NMR (approximately 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 approximately 5 Hz.
authors.affiliation: Irkutsk Institute of Chemistry, Favorsky Street 1, 664033 Irkutsk, Russia. sasha@irioch.irk.ru
authors.forename: Andrei V
authors.initials: AV
authors.lastname: Afonin
authors.forename: Igor A
authors.initials: IA
authors.lastname: Ushakov
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Vashchenko
authors.forename: Dmitry E
authors.initials: DE
authors.lastname: Simonenko
authors.forename: Andrei V
authors.initials: AV
authors.lastname: Ivanov
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Vasil'tsov
authors.forename: Al'bina I
authors.initials: AI
authors.lastname: Mikhaleva
authors.forename: Boris A
authors.initials: BA
authors.lastname: Trofimov