Dielectric relaxation and dipole moments of substituted pyrroles

Cumper, C. W. N.; Wood, J. W. M.

doi:10.1039/j29710001811

Cited by 17 publications

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“…Liquid pyrrole has been extensively studied by different authors [8][9][10][11]. Rahkamaa [8] has determined the 14N quadrupole relaxation time of pyrrole using Downloaded by [Nanyang Technological University] at 18:13 17 June 2016 the Pople theory [12].…”

Section: Introductionmentioning

confidence: 99%

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Nuclear relaxation, molecular motions and interactions

et al. 1977

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The t4N quadrupolar relaxation time for pyrrole as the pure liquid and in solution in 1,4-dioxan, pyridine, 3,5-1utidine and 2-fluoropyridine has been determined from the line-shape analysis of the imido proton magnetic resonance signal. The dependence of the line shape on solute concentration and temperature was studied and the activation parameters for molecular reorientation determined. INTRODUCTIONNuclear magnetic relaxation measurements can provide valuable information on molecular motions and interactions in liquids. However, the main difficulty in interpreting such information lies in the separation of the observed relaxation time into contributions from different mechanisms (e.g. dipole-dipole, scalar, spin-rotation) which arise from both intra and inter-molecular motions. The problem is considerably simplified [1, 2] if the nuclei under study are relaxed by the quadrupole mechanism, since this can be two or three orders of magnitude more efficient than competing mechanisms, including relaxation by dissolved oxygen. Furthermore, quadrupole relaxation is normally governed by intramolecular motions only, since the contributions of inter-molecular motions to the local electric-field gradients are very small and separation of translational effects is not needed.Many papers have dealt with studies of molecular motions in pure liquids but so far much less attention has been paid to strongly interacting systems such as those involving hydogen-bonded or charge-transfer interactions [3]. Mixtures of hydrogen-bonded liquids offer an interesting possibility for these studies.

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Section: Introductionmentioning

confidence: 99%

“…The relaxation times of pyrrole have been measured by both proton N.M.R. [9] and dielectric [10] relaxation methods. Recently Voelkel and Sillescu [11] have determined the anisotropy of rotational diffusion constants by deuteron relaxation time measurements.…”

Section: Introductionmentioning

confidence: 99%

Nuclear relaxation, molecular motions and interactions

et al. 1977

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Section: Journal Of Physical Chemistry and Biophysicsmentioning

confidence: 99%

“…ΔE cis/trans of 2-substituted pyrroles vary in a range of 1.06-8.04 kcal/mol. ΔE cis/trans of the N-H moieties (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) range from 1.06 to 5.15, whereas those of the N-CH 3 moieties [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] range from 1.93 to 8.08 kcal/mol. The lowest energy difference bacteria [9][10][11].…”

Section: Introductionmentioning

confidence: 99%

“…Kaye et al established, using a variable temperature experiment, that the synform of t-butyl pyrrole-2-carboxylate is thermo chemically more stable by 1.15 kcal/mol than the anti-form [30]. The effects of solvent such as benzene and dioxane on the dipole moments of planar conformers of 2-formyl-and 2-acetylpyrrole were investigated by Lumbroso [36] and Cumper [37] to establish the preferred conformation.Low-temperature 13 C NMR spectra were applied by Lunazzi [38] in the conformational study of thiophenecarbaldehydes. The activation energy for the conversion of the more stabz syn-form into the less stable anti-conformer is 10.1 kcal/mol for thiophene-2-carbaldehyde.…”

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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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Physical and Theoretical Aspects of 1H‐Pyrroles

Chadwick

1990

Chemistry of Heterocyclic Compounds: A Series of Monographs

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Dielectric relaxation and dipole moments of substituted pyrroles

Cited by 17 publications

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Nuclear relaxation, molecular motions and interactions

Nuclear relaxation, molecular motions and interactions

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

Physical and Theoretical Aspects of 1H‐Pyrroles

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