1H and 13C nmr study of conformational and electronic structure of 1-vinylpyrroles

Sigalov, M. V.; Трофимов, Б. А.; Михалева, А. И.; Калабин, Г. А.

doi:10.1016/s0040-4020(01)98921-5

Cited by 44 publications

(14 citation statements)

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“…In the isomers of aldoxime 2 the signal of the C(β) atom of the vinyl group is displaced towards low field compared with that for the isomers of 1-vinylpyrrole-2-carbaldoxime 1 (113.72 in the E-and 115.57 ppm in the Z-form of compound 2 compared with 100.56 in the E-and 104.04 ppm in the Z-form of compound 1). This means that in aldoxime 2 the vinyl group is brought out of the plane of the pyrrole ring due to the steric effects of the substituents neighboring the vinyl group, and the p-π conjugation with it is disturbed [23,24]. As a result of this, the π-donating ability of the pyrrole ring in aldoxime 2 is increased compared with aldoxime 1, and as mentioned above the intensity of its π,π-interaction with the -C=N-O fragment increases.…”

Section: *mentioning

confidence: 99%

Stereospecificity of shielding constants of carbon-13 nuclei in 13C NMR spectra of oximes of hetarenecarbaldehydes and alkyl heteryl ketones

Afonin

Ushakov

Simonenko

et al. 2008

Chem Heterocycl Comp

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It has been discovered that the chemical shifts of carbon atoms in 13 C NMR spectra of oximes having pyrrolyl, furyl, benzofuryl, thienyl, and pyridyl rings as substituents are changed systematically on going from the E-to the Z-isomer. This makes it possible to use the indicated chemical shifts for establishing the configuration of oximes with heterocyclic substituents and studying the special features of their electronic structure.Keywords: oximes with heterocyclic substituents, 13 C NMR spectra, stereospecificity of shielding constants.The stereospecificity of NMR spectral parameters of aldoximes and ketoximes has been studied for several decades . In particular it is necessary to select investigations of 1 H, 13 C, and 15 N spectra of oximes having a heterocyclic substituent. The 1 H NMR spectra of furfural oximes were investigated in the earlier studies [4,5]. The most interesting data were obtained for oximes enriched with 15 N isotope, in which a dependence was discovered of the geminal 15 N-1 H coupling constant on the steric orientation of the unshared pair of the nitrogen atom [5]. Ideas on the stereospecificity of parameters of 15 N NMR spectra in 15 N-labeled furfural oximes were developed in [9, 12], in which the stereospecificity of the 15 N nuclear shielding constants, the geminal 15 N-13 C coupling constants, and the vicinal 15 N-1 H coupling constants was shown. The aim of the present work was to study the stereospecificity of the shielding constants of the carbon-13 nuclei in 13 C NMR spectra of the series of oximes 1-6 having various heterocyclic substituents.The chemical shifts of 13 C atoms of oximes 1-6, and also of model oximes 7a,b, are given in Table 1. Two-dimensional 1 H-13 C correlation procedures HSQC and HMBC were used to assign the signals in the 13 C NMR spectra. Configurational assignment of aldoximes 1 and 2 was made on the basis of the differences of the chemical shift values of the "oxime" proton for the E-and Z-isomers, taking into account that in the E-isomer _______ * Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. __________________________________________________________________________________________

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confidence: 99%

Stereospecificity of shielding constants of carbon-13 nuclei in 13C NMR spectra of oximes of hetarenecarbaldehydes and alkyl heteryl ketones

Afonin

Ushakov

Simonenko

et al. 2008

Chem Heterocycl Comp

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“…However, the vinyl group adopts preferentially the trans position with respect to the alkyl substituent on the 2 position of the pyrrole ring, the coplanarity of unsaturated fragments being broken, and the presence of bulky substituents in this position causes a further increase in the dihedral angle between the planes of the vinyl group and the pyrrole ring . When the substituents are on the 2 and 5 positions of the pyrrole ring, the out‐of‐plane deviation of the vinyl group from the pyrrole ring becomes particularly significant, and the p, π ‐conjugation with the vinyl group is greatly disturbed . Violation of coplanarity of the vinyl and pyrrole moieties appears in the number characteristics of the 1 H and 13 C NMR spectra.…”

Section: Introductionmentioning

confidence: 99%

Experimental and theoretical study of the intramolecular C–H···N and C–H···S hydrogen bonding effects in the¹H and¹³C NMR spectra of the 2‐(alkylsulfanyl)‐5‐amino‐1‐vinylpyrroles: a particular state of amine nitrogen

Afonin

Павлов

Albanov

et al. 2013

Magnetic Reson in Chemistry

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In the (1)H NMR spectra of the 1-vinylpyrroles with amino- and alkylsulfanyl groups in 5 and 2 positions, an extraordinarily large difference between resonance positions of the HA and HB terminal methylene protons of the vinyl group is discovered. Also, the one-bond (1)J(C(β),H(B)) coupling constant is surprisingly greater than the (1)J(C(β),H(A)) coupling constant in pyrroles under investigation, while in all known cases, there was a reverse relationship between these coupling constants. These spectral anomalies are substantiated by quantum chemical calculations. The calculations show that the amine nitrogen lone pair is removed from the conjugation with the π-system of the pyrrole ring so that it is directed toward the HB hydrogen. These factors are favorable to the emergence of the intramolecular C-HB •••N hydrogen bonding in the s-cis(N) conformation. On the other hand, the spatial proximity of the sulfur to the HB hydrogen provides an opportunity of the intramolecular C-HB •••S hydrogen bonding in the s-cis(S) conformation. Presence of the hydrogen bond critical points as well as ring critical point for corresponding chelate ring revealed by a quantum theory of atoms in molecules (QTAIM) approach confirms the existence of the weak intramolecular C-H•••N and C-H•••S hydrogen bonding. Therefore, an unusual high-frequency shift of the HB signal and the increase in the (1)J(C(β),H(B)) coupling constant can be explained by the effects of hydrogen bonding.

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“…Systematic studies on the 1 H and 13 C NMR spectra of a wide series of pyrrole derivatives [1][2][3][4][5][6][7] allowed us to distinguish 2-hetarylpyrroles as a class of compounds giving rise to various intramolecular hydrogen bonds. For example, a weak intramolecular hydrogen bond CH · · · N between the -hydrogen atom of the vinyl group and pyridine nitrogen atom was found in 1-vinyl-2-(2-pyridyl)pyrrole [6].…”

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confidence: 99%

1H and 13C NMR Study of Bifurcated Intramolecular Hydrogen Bonds in 2,6-Bis(2-pyrrolyl)pyridine and 2,6-Bis(1-vinyl-2-pyrrolyl)pyridine

et al. 2005

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According to the 1 H and 13 C NMR data, bifurcated intramolecular hydrogen bond NH···N··· HN in 2,6-bis(2-pyrrolyl)pyridine fixes its molecule in a conformation with syn orientation of the pyrrole rings. An analogous bifurcated hydrogen bond CH · · · N · · · HC is formed in 2,6-bis(1-vinyl-2-pyrrolyl)pyridine. 2-(1-Vinyl-2-pyrrolyl)-6-(2-pyrrolyl)pyridine is characterized by unsymmetrical bifurcated hydrogen bond NH···N···HC.Systematic studies on the 1 H and 13 C NMR spectra of a wide series of pyrrole derivatives [1-7] allowed us to distinguish 2-hetarylpyrroles as a class of compounds giving rise to various intramolecular hydrogen bonds. For example, a weak intramolecular hydrogen bond CH · · · N between the -hydrogen atom of the vinyl group and pyridine nitrogen atom was found in 1-vinyl-2-(2-pyridyl)pyrrole [6]. 2-(2-Pyridyl)pyrrole is characterized by a weak intramolecular hydrogen bond NH···N between the pyrrole N-H atom and pyridine nitrogen atom [4]. The 1 H NMR and IR spectra of 5-(2-pyridyl)-2-trifluoroacetylpyrrole revealed a bifurcated hydrogen bond involving both pyridine nitrogen atom and carbonyl oxygen atom of the trifluoroacetyl group [4,5]. In continuation of our studies on intramolecular hydrogen bonds in pyrrole derivatives, in the present work we examined the 1 H and 13 C NMR spectra of 2,6-bis(2-pyrrolyl)pyridine (I) and 2,6-bis-(1-vinyl-2-pyrrolyl)pyridine (VI) and compared the results with those found for model compounds II-V and VII-XIV.The 1 H and 13 C NMR spectra of pyrroles I-XIV are given in Tables 1 and 2, and the 13 C-1 H coupling constants are collected in Table 3. Following the previously used algorithm for studying 2-hetarylpyrroles by NMR spectroscopy, let us consider first the character of , conjugation between the heterorings in compounds I and VI on the basis of the corresponding carbon chemical shifts. We showed in [4] that the signals from C 3' and C 5' in the pyridine ring of I-V, R 1 = H; I, R 2 = H; II, R 2 = 2-pyridyl; III, R 2 = 3-pyridyl; IV, R 2 = 4-pyridyl; V, R 2 = Ph; VI-XIII, R 1 = CH 2 =CH; VI, VII, R 2 = CH 2 =CH; VIII, R 2 = 2-pyridyl; IX, R 2 = 3-pyridyl; X, R 2 = 4-pyridyl; XI, R 2 = Ph; XII, XIII, R 2 = H. 3'2'

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1H and 13C nmr study of conformational and electronic structure of 1-vinylpyrroles

Cited by 44 publications

References 12 publications

Stereospecificity of shielding constants of carbon-13 nuclei in 13C NMR spectra of oximes of hetarenecarbaldehydes and alkyl heteryl ketones

Stereospecificity of shielding constants of carbon-13 nuclei in 13C NMR spectra of oximes of hetarenecarbaldehydes and alkyl heteryl ketones

Experimental and theoretical study of the intramolecular C–H···N and C–H···S hydrogen bonding effects in the¹H and¹³C NMR spectra of the 2‐(alkylsulfanyl)‐5‐amino‐1‐vinylpyrroles: a particular state of amine nitrogen

1H and 13C NMR Study of Bifurcated Intramolecular Hydrogen Bonds in 2,6-Bis(2-pyrrolyl)pyridine and 2,6-Bis(1-vinyl-2-pyrrolyl)pyridine

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1H and 13C nmr study of conformational and electronic structure of 1-vinylpyrroles

Cited by 44 publications

References 12 publications

Stereospecificity of shielding constants of carbon-13 nuclei in 13C NMR spectra of oximes of hetarenecarbaldehydes and alkyl heteryl ketones

Stereospecificity of shielding constants of carbon-13 nuclei in 13C NMR spectra of oximes of hetarenecarbaldehydes and alkyl heteryl ketones

Experimental and theoretical study of the intramolecular C–H···N and C–H···S hydrogen bonding effects in the1H and13C NMR spectra of the 2‐(alkylsulfanyl)‐5‐amino‐1‐vinylpyrroles: a particular state of amine nitrogen

1H and 13C NMR Study of Bifurcated Intramolecular Hydrogen Bonds in 2,6-Bis(2-pyrrolyl)pyridine and 2,6-Bis(1-vinyl-2-pyrrolyl)pyridine

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Experimental and theoretical study of the intramolecular C–H···N and C–H···S hydrogen bonding effects in the¹H and¹³C NMR spectra of the 2‐(alkylsulfanyl)‐5‐amino‐1‐vinylpyrroles: a particular state of amine nitrogen