C-13 NMR CHEMICAL-SHIFTS OF BETA-ALKOXYVINYL KETONES .3. EMPIRICAL SUBSTITUENT EFFECTS IN 1-ALKYLAMINO-6-ETHOXY-1,5-HEXADIEN-3,4-DIONES AND1,6-BIS(ALKYLAMINO)-1,5-HEXADIEN-3,4-DIONES

Evaluation by empirically derived equations for the substituent effect (E(Xn) and E(Yn) n=1 to 6) on the C-13 NMR chemical shifts for C-1, C -2, C-3, C-4, C-5 and C-6 in 1-alkylamino-6-ethoxy-1,5-hexadien-3,4-di ones 1a-f and 1,6-bis(alkylamino)-1,5-hexadien-3,4-diones 2a-f [XCH=CH C(O)C(O)CH=CHY, where X, Y=OEt, NH2, PhCH(2)NH, n-BuNH, i-PrNH, cyclo- C6H11NH, t-BuNH], taking as reference the 1,6-diethoxy-1,5-hexadien-3, 4-dione (3), is reported. From the calculated values for the E(Xn) and E(Yn) effects for each substituent it was possible to estimate the ch emical shift of each carbon of the compounds 1,2 with excellent precis ion: 100% of the calculated chemical shifts are found to be within +/- 0.5ppm. The carbon-13 chemical shifts of C-1, C-2 and C-3 of compounds 1a,2a,3 led a good correlation with carbon charge densities (qr).