Deuterium Isotope Effects on 13C Chemical Shifts of Enaminones.
作者:Donka Kh. Zheglova、Daniel G. Genov、Simon Bolvig、Poul Erik Hansen、M. Hanfland、E. Dooryhee
DOI:10.3891/acta.chem.scand.51-1016
日期:——
Deuterium isotope effects on C-13 chemical shifts have been studied in a series of substituted N-alkyl and N-phenyl keto-enamines. The intramolecularly hydrogen bonded Z-forms show the largest two-bond isotope effects, (2) Delta C-1(ND). Methyl-substitution al C-l leads to a larger two-bond isotope effect in the N-phenyl-substituted derivatives. This effect is ascribed to steric compression. Space-filling substituents at the ortho-position of the N-phenyl ring lead to a decrease of the two-bond isotope effect. A correlation is found between (2) Delta C-1(ND) and (3) Delta C-2'(ND). The latter becomes negative in the sterically hindered cases. (3) Delta C-2'(ND) may therefore be used as a gauge of the twist of the phenyl ring.o-Hydroxy substitution of the CO-phenyl rings enables intramolecular hydrogen bonding to the carbonyl group. This kind of hydrogen bond with two donors to one acceptor leads to smaller (2) Delta C-2(ND) and (2) Delta C-2 ''(OD) isotope effects equivalent to weaker hydrogen bonds for the Z-isomer. This is ascribed to competition for the acceptor. For the E-isomer (2) Delta C(OD) is enhanced. The same feature is seen for N,N-dimethylamino enamines. This increase is ascribed to delocalization of the nitrogen lone-pair onto the carbonyl oxygen, thereby strengthening the hydrogen bond and thus leading to larger two-bond, (2) Delta C(OD), isotope effects.
Garnovskii, A. D.; Abramenko, V. L., Journal of general chemistry of the USSR, 1985, vol. 55, p. 1630 - 1636
作者:Garnovskii, A. D.、Abramenko, V. L.
DOI:——
日期:——
NMR of Enaminones Part 3—1H,13C and17O NMR Spectroscopic Studies of Acyclic and CyclicN-Aryl Enaminones: Substituent Effects and Intramolecular Hydrogen Bonding
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