Spectroscopic and theoretical studies on the aromaticity of pyrrol-2-yl-carbonyl conformers

Dubis, Alina T.; Wojtulewski, Sławomir; Filipkowski, Karol

doi:10.1016/j.molstruc.2013.02.030

Cited by 8 publications

(8 citation statements)

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“…The introduction of the -NH 2 group as R leads to substantial double bond localization in the pyrrole ring and in consequence to a decrease in its aromaticity. In the case of a chloro substituent (R=14-19 and 33-38), an increase in aromaticity of the pyrrole ring was observed [51]. It is in good agreement with the barrier height ( Table 1).…”

Section: Internal Rotation About the C-c Bondsupporting

confidence: 81%

“…We can state that this phenomenon results from more effective π-electron delocalization. This was very evidently shown by HOMA aromaticity indices [51]. The data point out that there is a trend that HOMAs for syn conformers are higher than those for anti-conformers.…”

Section: Internal Rotation About the C-c Bondmentioning

confidence: 70%

“…The barrier heights for those reactions vary from 7.03 to 16.21 kcal/mol depending on the R substituent group. On the basis of previous studies [50,51], we noted that the electrondonating substituent slightly destabilizes the ring system, affecting the aromaticity of the pyrrole ring. The introduction of the -NH 2 group as R leads to substantial double bond localization in the pyrrole ring and in consequence to a decrease in its aromaticity.…”

mentioning

confidence: 70%

“…For the more stable syn and anti planar configurations the C-C bond has a more double bond character due to resonance which keeps the carbonyl group in the same plane as the pyrrole ring. The theoretically calculated geometrical parameters of 2-acylpyrroles [51] clearly reveal elongation of the (C2) carboncarbon (C=O) bond for anti compared with syn-conformers. These observations suggest relatively larger stability of the syn-conformer than its anti counterpart.…”

Section: Internal Rotation About the C-c Bondmentioning

confidence: 96%

“…The structural parameters obtained from optimized geometries (B3LYP/6-311++G(d,p)) for the syn and anti-conformers of 2-acylpyrroles were published in 2013 [51].…”

Section: Internal Rotation About the C-c Bondmentioning

confidence: 99%

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Conformational Preferences of 2-Acylpyrroles in Light of FT-IR and DFT Studies

Dubis

2014

J Phys Chem Biophys

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2-carboxylic acids [3] and corresponding esters [4]. Pyrrole-2-carboxylates are also useful substrates for the preparation of more complex pyrrole containing systems [5] such as ketorolac, a drug with anti-inflammatory and analgesic properties [6]. It is noted that the 2-acylpyrrole motif is widespread in nature. There are many examples of 2-acylpyrrole based molecules (Figure 1) with various biological activities [7,8]. Representative examples are pyoluteorin and pyrrolomycin D, secondary metabolites produced by marine Conformational Preferences of 2-Acylpyrroles in Light of FT-IR and DFT StudiesAlina T Dubis* Institute of Chemistry, University of Białystok, Hurtowa 1, Poland AbstractConformations of alpha-substituted pyrroles have been effectively studied using spectroscopic methods assisted by theoretical calculations developed in the recent decade. The question of how to effectively study the conformation of 2-acylpyrrole no longer remains unanswered. The detailed spectroscopic studies conducted in the last decade and interpreted on the basis of theoretical calculations provide a satisfactory answer to that question. Based on the Density Functional Theory (DFT) calculations of conformational properties of 2-acylpyrroles, for which two stable rotameric forms were predicted, syn and anti-conformers have been studied either by experimental or theoretical methods. The family of 2-acylpyrroles have both a proton donor N-H group and a proton acceptor C=O group. This structure favors the formation of doubly hydrogen-bonded cyclic dimers connected by two N-H...O=C bonds. The tendency to form cyclic dimers stabilizes the syn-conformation. Due to these properties 2-acylpyrroles can be used as structural models for the conformational analysis of peptides.This review summarizes recent investigations of conformations of 2-acylpyrroles, with a particular emphasis on the hydrogen bonds forming within these systems. The influence of 2-substitution on different aspects of stability of these molecular systems and the usefulness of infrared spectroscopy supported by theoretical calculations in H-bonds and conformational studies are discussed. Among the molecular properties hydrogen bond energy, structural characteristics such as C=O bond length of dimers and unique spectral features of 2-acylpyrroles that can be used to predict and investigate the conformation and structure of proteins are considered.Graphical abstract. The potential energy diagram of 2-acylpyrroles as a function of the dihedral angle pyrrole ringcarbonyl group of bond rotation. Most stable conformer syn converts to conformer anti via the transition state TS1; less stable conformer anti converts to conformer syn via the transition state TS2. conformational research and can greatly support experimental work with quite good accuracy. Among the most useful parameters are geometrical parameters, relative conformational energies, barriers to internal rotation and vibrational frequencies for each conformer. Journal of Physical Chemistry & BiophysicsEnergy differ...

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Section: Internal Rotation About the C-c Bondsupporting

confidence: 81%

Section: Internal Rotation About the C-c Bondmentioning

confidence: 70%

mentioning

confidence: 70%

Section: Internal Rotation About the C-c Bondmentioning

confidence: 96%

“…The structural parameters obtained from optimized geometries (B3LYP/6-311++G(d,p)) for the syn and anti-conformers of 2-acylpyrroles were published in 2013 [51].…”

Section: Internal Rotation About the C-c Bondmentioning

confidence: 99%

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