Microwave spectra of isotopic pyrroles. Molecular structure, dipole moment, and 14N quadrupole coupling constants of pyrrole

Nygaard, Use; Nielsen, Jørgen Tormod; Kirchheiner, Jørgen; Maltesen, Gudrun; Rastrup‐Andersen, John; Sørensen, Georg

doi:10.1016/0022-2860(69)80031-1

Cited by 284 publications

(113 citation statements)

References 18 publications

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“…The determined parameters for the ground state are in agreement with the structure characterized experimentally from microwave spectra of isotopic pyrroles. 38 The geometry optimizations, performed numerically at the CASPT2 level for each of the states, were restricted to the planar C 2v symmetry. As shall be discussed below, the computed CASPT2 force fields confirm the planar, C 2v , character of the ground and four Rydberg states.…”

Section: Resultsmentioning

confidence: 99%

Theoretical characterization of the lowest-energy absorption band of pyrrole

Roos

Malmqvist

Molina

et al. 2002

The Journal of Chemical Physics

122

145

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The lowest-energy band of the electronic spectrum of pyrrole has been studied with vibrational resolution by using multiconfigurational second-order perturbation theory ͑CASPT2͒ and its multistate extension ͑MS-CASPT2͒ in conjunction with large atomic natural orbital-type basis sets including Rydberg functions. The obtained results provide a consistent picture of the recorded spectrum in the energy region 5.5-6.5 eV and confirm that the bulk of the intensity of the band arises from a * intravalence transition, in contradiction to recent theoretical claims. Computed band origins for the 3s,3p Rydberg electronic transitions are in agreement with the available experimental data, although new assignments are suggested. As illustrated in the paper, the proper treatment of the valence-Rydberg mixing is particularly challenging for ab initio methodologies and can be seen as the main source of deviation among the recent theoretical results as regards the position of the low-lying valence excited states of pyrrole.

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Section: Resultsmentioning

confidence: 99%

Theoretical characterization of the lowest-energy absorption band of pyrrole

Roos

Malmqvist

Molina

et al. 2002

The Journal of Chemical Physics

122

145

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“…The ring coordinates were based on the microwave structure of pyrrole (8) coupled with the force-field structure for cyclopentene (9).…”

Section: Ring Conformationsmentioning

confidence: 99%

The conformational analysis of piriprost, an inhibitor of leukotriene synthesis, based on high-field nuclear magnetic resonance studies

Kotovych¹,

Beierbeck²,

Salmon³

1985

Can. J. Chem.

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GEORGE KOTOVYCH, HELMUT BEIERBECK, and DAVID SALMON. Can. J. Chem. 63, 2614 (1985). The analysis of proton nuclear Overhauser effect data for piriprost, (6,9-deepo~~)-6,9-(phenylimino)-A~~~ prostaglandin 11, indicates that the cyclopentene ring has the "E conformation. A long-range nOe effect indicates that the a-chain is folded near the pyrrole and the phenyl rings. GEORGE KOTOVYCH, HELMUT BEIERBECK et DAVID SALMON. Can. J. Chem. 63, 2614(1985. Une analyse des donnCes relatives h l'effet Overhauser nuclCaire du proton pour le piriprost, dCCpoxy-6,9 phtnylimino-6,9 A6.8-prostaglandine I,, indique que le noyau cyclopentkne existe dans la conformation "E. Un effet eon h longue distance indique que la chaine a est repliCe prks des noyaux pyrrole ainsi que phtnyle.[Traduit par le journal]The leukotrienes are the products of the metabolism of arachidonic acid, which proceeds via two enzymatic processes. Cyclooxygenase transforms arachidonic acid to the prostaglandins, the thromboxanes, and prostacyclin, whereas lipoxygenases give rise to the leukotrienes. The properties and syntheses of the leukotrienes have been well reviewed (1, 2). The leukotrienes may be separated into two categories. The first series consists of leukotrienes C4, D4, and E4, which collectively account for the biological activity ascribed to Slow Reacting Substances of Anaphylaxis. These compounds may therefore be important mediators of human diseases such as bronchial asthma. The second series consists of 5,12-dihydroxyeicosatetraenoic acids and one of these is leukotriene B,, which is a potent stimulator ofthe movement of the leucocytes in vitro.Over the last few years, we have been interested in the conformational analysis of the prostaglandins and leukotrienes (3,4) as well as in quantitative nuclear Overhauser effect (nOe) studies as applied to flexible systems. In the course of these studies, we have analyzed nuclear Overhauser effect data for piriprost (6,9-deepoxy)-6,9-(pheny1imino)-A6' prostaglandin I, ( 3 , an inhibitor of leukotriene synthesis (Fig. 1). The quantitative analysis of the nOe data indicates the presence of a long-range interaction between the H-2 protons of the a chain and the pyrrole as well as the phenyl protons. These results will lead to a better understanding of structure-activity relationships. ExperimentalPiriprost was a gift from the Upjohn Company, in Kalamazoo, Michigan. The sample was prepared in glycine-d6 buffer in D20, pH 9.95. The sample was frozen on the vacuum rack, the D20 was removed, and fresh 100% D20 was vacuum distilled into the nmr tube. The sample was then degassed, using the freeze-pump-thaw technique, and sealed. The solution concentration was -0.005 M to minimize intermolecular association. About 5% EDTA was added to the solution. All glassware was cleaned extensively, including a nitric acid wash, to eliminate paramagnetic impurities.All nmr measurements were carried out on a Bruker WH-400 FT nmr spectrometer equipped with an Aspect 2000 data system, using 16K, 32K, or 64K of memory, as require...

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“…As a preliminary to the interstellar search, it was necessary to study several low J absorptions ofpyrrole in the laboratory. The microwave spectrum, including the nitrogen quadrupole analysis,was published by Nygaard et al (1969) but during our study of the Ill-ItO transition it became evident that the multiplet structure of the absorption could not be accurately predicted using the published microwave data. We therefore decided to study several multiplets of pyrrole in order to obtain more accurate values of the nitrogen quadrupole coupling constants.…”

mentioning

confidence: 90%

“…Fig. 1 shows an experimental tracing of the 1 11 -1 10 multiplet together with computersimulated plots obtained using (A) the above coupling constants and (B) the coupling constants of Nygaard et al (1969). Even on the scale of Fig.…”

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Study of Potential Interstellar Molecules: Nuclear Quadrupole Coupling Constants of the Nitrogen Atom in Pyrrole

Bolton¹,

Brown²

1974

Aust. J. Phys.

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The nuclear quadrupole coupling constants of the nitrogen atom in pyrrole have been redetermined by analysis of the hyperfine structure for several low J rotational transitions. The resulting values arex"" = 1'400±O'OO8 MHz and Xbb = 1·300±O·OO8 MHz. Small modifications to the previously reported rotational constants are given.Recent interest in the discovery of molecules in interstellar space led us to investigate the possibility of finding pyrrole, a simple heterocyclic compound containing atoms of only carbon, hydrogen and nitrogen. The importance of pyrrole in relation to the exobiology of porphyrins has recently been emphasized and a plea made for a search in the region of Sagittarius (Hodgson 1971). As a preliminary to the interstellar search, it was necessary to study several low J absorptions ofpyrrole in the laboratory. The microwave spectrum, including the nitrogen quadrupole analysis,was published by Nygaard et al. (1969) but during our study of the Ill-ItO transition it became evident that the multiplet structure of the absorption could not be accurately predicted using the published microwave data. We therefore decided to study several multiplets of pyrrole in order to obtain more accurate values of the nitrogen quadrupole coupling constants.Pyrrole (Koch-Light. pure grade) was used without further purification. Spectra were recorded using a conventional 5 kHz Stark-modulated G band spectrometer. Frequency measurements were made with a Hewlett-Packard 5246L electronic counter which was calibrated periodically against a Sulzer 2· 5C laboratory standard. Absolute frequencies of hyperfine components are quoted to an accuracy of ± 10kHz whereas frequency differences, between various components of the multiplet, can be determined to within ± 5 kHz. The pyrrole sample was contained in a dry-ice cooled absorption cell at pressures of approximately 1 J.tmHg (0'13 Pa). Time constants of the orders of 1 s were used whilst scanning the multipiets.A maximum resolution of 20 kHz half-width was achieved for the l 1C 1 10 transition. Substitution of the frequency separation between successive members of this multiplet into the well-known relationship of Casimir (1936)

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Microwave spectra of isotopic pyrroles. Molecular structure, dipole moment, and 14N quadrupole coupling constants of pyrrole

Cited by 284 publications

References 18 publications

Theoretical characterization of the lowest-energy absorption band of pyrrole

Theoretical characterization of the lowest-energy absorption band of pyrrole

The conformational analysis of piriprost, an inhibitor of leukotriene synthesis, based on high-field nuclear magnetic resonance studies

Study of Potential Interstellar Molecules: Nuclear Quadrupole Coupling Constants of the Nitrogen Atom in Pyrrole

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