title: Structural peculiarities of configurational isomers of 1-styrylpyrroles according to 1Н, 13С and 15N NMR spectroscopy and density functional theory calculations: electronic and steric hindrance for planar structure.
abstract: Comparative analysis of the (1)Н and (13)С NMR data for a series of the E and Z-1-styrylpyrroles, E and Z-1-(1-propenyl)pyrroles, 1-vinylpyrroles and styrene suggests that the conjugation between the unsaturated fragments in the former compounds is reduced. This is the result of the mutual influence of the donor p-π and π-π conjugation having opposite directions. According to the NMR data combined with the density functional theory calculations, the Z isomer of 1-styrylpyrrole has essentially a nonplanar structure because of the steric hindrance. However, the E isomer of 1-styrylpyrrole is also an out-of-plane structure despite the absence of a sterical barrier for the planar one. Deviation of the E isomer from the planar structure seems to be caused by an electronic hindrance produced by a mutual influence of the p-π and π-π conjugation. The structure of the E isomer of the 2-substituted 1-styrylpyrroles is similar to that of the 2-substituted 1-vinylpyrroles. The steric effects in the Z isomer of the 2-substituted 1-styrylpyrroles result in the large increase of the dihedral angle between planes of the pyrrole ring and double bond.
authors.affiliation: Institute of Chemistry, Siberian Branch of the Russian Academy of Science, Favorski St 1, 664033 Irkutsk, Russia.
authors.forename: Andrei V
authors.initials: AV
authors.lastname: Afonin
authors.forename: Igor A
authors.initials: IA
authors.lastname: Ushakov
authors.forename: Dmitry V
authors.initials: DV
authors.lastname: Pavlov
authors.forename: Elena Yu
authors.initials: EY
authors.lastname: Schmidt
authors.forename: Marina Yu
authors.initials: MY
authors.lastname: Dvorko
mesh_terms: D002247:Carbon Isotopes; D004583:Electrons; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009587:Nitrogen Isotopes; D011522:Protons; D011758:Pyrroles / Q000737:chemistry*; D011789:Quantum Theory; D013237:Stereoisomerism
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D011522:Protons; D011758:Pyrroles