- NMR of enaminones part 3 ? - 1H, 13C and 17O NMR spectroscopic studies of acyclic and cyclic N-aryl enaminones: Substituent effects and intramolecular hydrogen bonding
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17O, 13C and 1H NMR spectra for para-and meta-substituted 4-arylaminopent-3-en-2-ones (acyclic enaminones, 1 and 2) and 3-arylaminocyclohex-2-en-1-ones (cyclic enaminones, 3 and 4) are reported. The 17O, 13C and 1H shift values of these enaminones correlate well with σm0 and σp- constants in the correlations for meta and para derivatives, and with pKa values of the corresponding anilines. Dual substituent parameters analyses were also performed. Correlations of 17O and 13C chemical shifts of the carbonyl groups with those of the corresponding N-acylanilines indicate that the enaminone moiety as a whole has electronic properties similar to those of the RCONH group. The 17O shift values of the carbonyl O atoms of enaminones correlate well with their 1H and 13C data. Shieldings of 33-45 ppm for O atoms are observed for 1 and 2 compared with 3 and 4, respectively. This is attributed to intramolecular hydrogen bonding.
- Zhuo, Jin-Cong
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p. 311 - 322
(2007/10/03)
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