NMR of enaminones .4. O-17 NMR study of 2,2-diacylenamines

Natural abundance 170 NMR spectra of 41 2,2-diacylenamines (enamino diketones and enamino diesters), recorded in acetonitrile solution, are reported. Tertiary enamino diketones show only one O-17 signal; primary and secondary derivatives show two O-17 signals. The shift difference (Delta delta(HB)) between the two carbonyl groups is mainly attributed to intramolecular hydrogen bonding and depends on the donor property of the amino group and the structure of the enamino diketone. The delta(O-17) values correlate well with the pK(a) values of amines. Correlations of delta(O-17-1) values for the chelated carbonyl group with their delta(C-13-1) and delta(C-13-2) values are observed. (C) 1997 by John Wiley & Sons, Ltd.