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Digitale Medien

Kombinierte d-NMR- und LIS-Untersuchungen zum konformativen Verhalten von Formylmethylenthiopyranen (1983)

Kretschmer, Matthias ; Kleinpeter, E. ; Pulst, M. ; [weitere]

Springer

Monatshefte für Chemie 114 (1983), S. 289-302

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ISSN: 1434-4475

Schlagwort(e): Formylmethylenthiopyranes ; LIS-method ; Rotational barriers

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie

Notizen: Abstract The rotational barriers ΔG ≠ toE,Z- ands-cis, s-trans-isomerisation in formylmethylenthiopyranes are determined and discussed with regard to their dependence on substituent effects. Preferential conformers are distinguished by lanthanide induced shifts. Best fits between calculated and experimental shifts are obtained forE,s-trans andZ,s-cis isomers. The results indicate a nonbonding interaction between aldehyde oxygen and ring sulphur, favourings-cis conformation in case ofZ configuration.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00798952

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Digitale Medien

Dynamic NMR study of the electronic state of heteroaromatics. VFor Part IV, see Ref. 4. - Influence of the counter anion, ortho substituents and the ring heteroatom on the exocyclic C,N rotational barrier of pyrylium and thiopyrylium salts (1989)

Kleinpeter, E. ; Spitzner, R. ; Schroth, W.

Chichester : Wiley-Blackwell

Organic Magnetic Resonance 27 (1989), S. 713-718

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ISSN: 0749-1581

Schlagwort(e): Rotational barriers ; 1H NMR spectra ; Partial double bond character ; Mesomerism in pyrylium and thiopyrylium salts ; Chemistry ; Analytical Chemistry and Spectroscopy

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: The 13C NMR spectra and variable-temperature 1H NMR spectra of some NR2-substituted pyrylium and thiopyrylium salts were studied, and the rotational barriers thus obtained about the exocyclic partial C—N double bonds are discussed according to their dependence on the counter anion and other structural variations. The counter anion has a negligible influence on the barrier, but substituents on the ring can either strengthen electronically or weaken sterically the mesomerism of the NR2-heteroaromatic system. The competition between these two effects is readily estimated from the rotational barriers obtained. The pyrylium salts display higher rotational barriers than the identically substituted thiopyrylium salts.

Zusätzliches Material: 2 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/mrc.1260270802

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Digitale Medien

Stereochemistry of benzannelated 1,6-diazabicyclo[4.2.1]octadienes and the conformation of substituents on the methylene bridge (1990)

Kleinpeter, E. ; Hartmann, J. ; Werner, B. ; [weitere]

Chichester : Wiley-Blackwell

Organic Magnetic Resonance 28 (1990), S. 423-425

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ISSN: 0749-1581

Schlagwort(e): Stereochemistry ; 1,6-Diheterobicyclo[4.2.1]octa-3,7-dienes ; W-coupling ; NOE ; Chemistry ; Analytical Chemistry and Spectroscopy

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: The stereochemistry of benzannelated 1,6-diazabicyclo[4.2.1]octa-3,7-dienes (the conformation of the eight-membered ring and of the variable substituents on the methylene bridge) was determined by means of NOE enhancements and stereospecific long-range H,H coupling constants in the relevant NMR spectra.

Zusätzliches Material: 1 Tab.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/mrc.1260280508

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Digitale Medien

Dynamic NMR study of the electronic state of heteroaromatics. IIIFor Part I, see Ref. 3; for Part II, see Ref. 18. - Pyrylium salts or intramolecularly bridged pentamethine cyanines? (1988)

Kleinpeter, E. ; Spitzner, R. ; Schroth, W. ; [weitere]

Chichester : Wiley-Blackwell

Organic Magnetic Resonance 26 (1988), S. 707-713

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ISSN: 0749-1581

Schlagwort(e): Rotational barriers ; π-electron density alternation ; Mesomerism in pyrylium salts ; Chemistry ; Analytical Chemistry and Spectroscopy

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: The 13C NMR spectra and the temperature-dependent 1H NMR spectra of a series of NR2-substituted pyridines and pyrones were studied, and the 13C chemical shifts and the rotational barriers about the exocyclic partial C,N double bonds were compared with the corresponding values for suitable pyridinium, pyrylium and thiopyrylium salts. The NMR spectroscopic results are discussed in the light of the electronic state and mesomerism in the species studied; the salts in question should be named, from the electronic point of view, more realistically as bridged pentamethine cyanines rather than pyridinium, pyrylium and thiopyrylium salts.

Zusätzliches Material: 3 Tab.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/mrc.1260260813

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Digitale Medien

Restricted rotations about exocyclic partial double bonds. The electronic state of heteroaromatic six-membered rings (1987)

Kleinpeter, E. ; Spitzner, R. ; Schroth, W.

Chichester : Wiley-Blackwell

Organic Magnetic Resonance 25 (1987), S. 688-695

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ISSN: 0749-1581

Schlagwort(e): 13C NMR ; Temperature dependent ; 1HNMR spectra ; Pyrylium/thiopyrylium salts ; Pyrones/thiopyrones ; Rotational barriers ; Partial double bond character ; Chemistry ; Analytical Chemistry and Spectroscopy

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: Temperature-dependent 13C and 1H NMR spectra of three series of six-membered heteroaromatic systems with NR2 substituents attached to pyrylium/thiopyrylium salts and pyrones/thiopyrones have been recorded. The rotational barriers thus determined about the exocyclic partial double bonds are discussed in terms of dominating mesomeric structures, in order to describe the electronic state and the spatial conditions in the molecular framework. Cyanine and merocyanine substructures have been identified by NMR and express the electronic state predominantly present in the compounds.

Zusätzliches Material: 2 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/mrc.1260250807

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