ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The pulse sequence INEPT was used to obtain proton-coupled 15N-NMR spectra in natural isotope abundance for enamines substituted in 2-position with electron-with-drawing groups.The chemical shifts and coupling constants are discussed in terms of their relationship to structural features such as multiple N-alkyl substitution, double-bond configuration, H-bonding, N-lone-pair delocalization within the conjugated system, and steric effects.It is concluded that 15N chemical shifts are a sensitive probe for local structural modifications at the N-atom and conformational changes in a remote part of a conjugated molecule, while one-bond N,H-coupling essentially reflects N-hybridization and subtle local geometric distortions. Stereospecific three-bond N,H spin coupling to olefinic protons (4.0 ± 0.2 Hz) has been found a characteristic feature of (Z)-isomers in all investigated compounds, whereas two-bond coupling to olefinic protons (2J(N,H) = 0.5 to 5 Hz) is observed in (E)-isomers. The sensitivity to solvents and steric properties of remote substituents renders geminal coupling a useful probe for studying electronic effects in the C—N bond.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19830660722
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