Study of conformations and hydrogen bonds in the configurational isomers of pyrrole‐2‐carbaldehyde oxime by ¹H, ¹³C and ¹⁵N NMR spectroscopy combined with MP2 and DFT calculations and NBO analysis

Abstract

The (1)H, (13)C and (15)N NMR studies have shown that the E and Z isomers of pyrrole-2-carbaldehyde oxime adopt preferable conformation with the syn orientation of the oxime group with respect to the pyrrole ring. The syn conformation of E and Z isomers of pyrrole-2-carbaldehyde oxime is stabilized by the N-H...N and N-H...O intramolecular hydrogen bonds, respectively. The N-H...N hydrogen bond in the E isomer causes the high-frequency shift of the bridge proton signal by about 1 ppm and increase the (1)J(N, H) coupling by approximately 3 Hz. The bridge proton shows further deshielding and higher increase of the (1)J(N, H) coupling constant due to the strengthening of the N-H...O hydrogen bond in the Z isomer. The MP2 calculations indicate that the syn conformation of E and Z isomers is by approximately 3.5 kcal/mol energetically less favorable than the anti conformation. The calculations of (1)H shielding and (1)J(N, H) coupling in the syn and anti conformations allow the contribution to these constants from the N-H...N and N-H...O hydrogen bondings to be estimated. The NBO analysis suggests that the N-H...N hydrogen bond in the E isomer is a pure electrostatic interaction while the charge transfer from the oxygen lone pair to the antibonding orbital of the N-H bond through the N-H...O hydrogen bond occurs in the Z isomer.

Soluble fluorescent polymeric nanoparticles based on pyrrole derivatives: synthesis, characterization and their structure dependent sensing properties

“…In order to investigate the effect of N-substitution on the sensing behaviour of polymer nanoparticles different chemical reagents were introduced into the polymer nanoparticles solutions and the changes in fluorescence signals were recorded. The pyrrole ring also have a soft character and can form hydrogen bonds through its N-H group 60 . 10a shows the effect of 5 µM of thiram and 50 µM of other chemical compounds on the fluorescence signal of PPy nanoparticles in chloroform.…”

2‐(Hydroxyimino)aldehydes: Photo‐ and Physicochemical Properties of a Versatile Functional Group for Monomer Design

“…The photoinduced switch of the E/Z configurationi ni mines, oximes and hydrazones has been extensively investigated in the field of light-driven molecular machines (see Ref. This interaction, whichi sa lso influenced by the nature and bulk of the Rg roup, has been studied for other 2-substituted oximes, such as a-keto-oximes, [13] monoterpenoid oximes, [14] pyrrole-2-carbaldehyde oxime, [15] nitrosation products of phosphoryl aldehydes, [16] and a-cyanoximes. In the case of HIAs, the aldehyde group has the highest priority,s oE/Z isomerism relates to the relative positions of the oxime OH and aldehyde groups about the oxime double bond (Figure 1a).…”

Stereospecificity of 13C shielding constants in acetone azine as a tool for configurational assignment of ketone azines

“…carbon chemical shifts of ketone oximes with various substituents [3][4][5][6][7][19][20][21][22]. As follows from the experimental data and the results of quantum-chemical calculations, stereochemical behavior of the parameters δ C and 1 J CC of acetone azine (I) and acetone oxime (II) conforms to a common relation.…”

“…As shown previously, analysis of stereochemical dependences of 1 H and 13 C shielding constants is a promising method for studying steric and electronic structures of compounds having an azomethine group [3][4][5][6][7]. Therefore, in the present work we examined the 13 C NMR spectrum of acetone azine and measured direct 13 C-13 C coupling constants in its molecule with a view to find indicator parameters ensuring simple and reliable assignment of configuration of ketazines.…”