An analysis of the 13C n.m.r. spectra of pyridazin-3-ones and some specifically deuteriated derivatives

Abstract

Optimum conditions are reported for the formation of [4-²H]- and [6-²H]-pyridazin-3(2H)-ones by gas-phase decarboxylation of the corresponding [²H]carboxylic acids or by cyclisation of the appropriate [N-²H]- or [3-²H]-5-(1,2-diazabutadien-4-ylidene)-2,2-dimethyl-1,3-dioxan-4,6-dione. By the use of deuteriated derivatives, the ¹³C n.m.r. parameters of pyridazin-3(2H)-one are assigned as follows: C(3),δ 164.00 (³J_CH 8.6 Hz); C(4), δ 130.45 (¹J_CH 171.9, ³J_CH 6.1 Hz); C(5), δ 134.71 (¹J_CH 168.3, ²J_CH(6) 8.0 Hz); C(6), δ 139.02 (¹J_CH 188.9, ²J_CH 2.7, ³J_CH(4) 7.9 Hz). Chemical shifts and coupling constants of a range of C-methyl-, N-t-butyl-, and N-aryl-pyridazin-3(2H)-ones are reported, and the substituent effects are correlated with model systems.