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Deuterium isotope effects on 13C chemical shifts of intramolecularly hydrogen-bonded olefins (1995)

Hansen, P. E. ; Bolvig, S. ; Duus, F. ; [weitere]

Chichester : Wiley-Blackwell

Organic Magnetic Resonance 33 (1995), S. 621-631

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ISSN: 0749-1581

Schlagwort(e): NMR ; 13C NMR ; isotope effects on 13C chemical shifts ; deuterium isotope effects ; intramolecular hydrogen bonding ; hydrogen bond strength ; olefins ; β-sulphinylenamines ; nitroenamines ; β-diketones (five-membered ring) ; Chemistry ; Analytical Chemistry and Spectroscopy

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: A series of intramolecularly hydrogen-bonded enamines, enols and enethiols with ester carbonylic, ketonic carbonylic, thioester carbonylic, nitro and sulphoxide acceptors were investigated to obtain 13C chemical shifts and deuterium isotope effects. Results from 33 new compounds and six remeasurements are compared with already existing data. An important aim was to show that isotope effects on chemical shifts are useful descriptors of hydrogen-bonded systems and not only a parameter proportional to the 13C chemical shifts. Substituent effects were studied and the donors and acceptors ranked according to their abilities to support hydrogen bonding. Steric effects strengthen the hydrogen bonding in cyclic five-membered β-diketones. Plots of two-bond [2ΔC(OD)] vs. four-bond isotope effects [4ΔC(OD)] show that 4ΔC(OD) increases with increasing hydrogen bond strength and that large deviations from this relationship can be an indicator of tautomerism.

Zusätzliches Material: 8 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/mrc.1260330803

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Digitale Medien

Data for the characterization of the geometrical isomers of β-sulphinylenamines (1994)

Kozerski, L. ; Kawȩcki, R. ; Hansen, P. E.

Chichester : Wiley-Blackwell

Organic Magnetic Resonance 32 (1994), S. 517-524

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ISSN: 0749-1581

Schlagwort(e): β-Sulphinylenamines ; Geometrical isomerism ; NH chemical shifts ; Temperature effects ; 15N chemical shifts ; Chemistry ; Analytical Chemistry and Spectroscopy

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: NOE experiments at low temperature were used to establish the structure of the E- and Z-isomers of the enamine ButSOCH=CHNHBut. The NOE experiments revealed large intermolecular NOE effects between E- and Z-isomers indicating the formation of dimers of specific orientation. NH chemical shifts and their temperature dependence showed that the E- and Z- isomers behave differently. The NH chemical shifts of the former go to higher frequencies on lowering the temperature, whereas the opposite holds for the (Z)-NH resonance. Similar trends are found on increasing the concentration. The orientation around the C1—N bond can be probed by 3J(H1,NH) or by 1J(N,H). The 15N chemical shifts were also investigated in a series of β-sulphinylenamines. They are mainly dominated by α- and β-effects and show only a slight dependence on the E/Z isomerism, which seems to indicate a weak hydrogen bond in the Z-isomer at high concentration. Pertinent NMR parameters are now available for a general structure determination of geometrical isomers of β-sulphinylenamines.

Zusätzliches Material: 1 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/mrc.1260320904

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