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 (3JCH 8.6 Hz); C(4), δ 130.45 (1JCH 171.9, 3JCH 6.1 Hz); C(5), δ 134.71 (1JCH 168.3, 2JCH(6) 8.0 Hz); C(6), δ 139.02 (1JCH 188.9, 2JCH 2.7, 3JCH(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.