Substituent and solvent effects on tautomeric equilibria of barbituric acid derivatives and isoterically related compounds
作者:Misa V. Jovanovic、Edward R. Biehl
DOI:10.1002/jhet.5570240136
日期:1987.1
N-Mono and N,N-dialkyl/diarylbarbituric acids exist in solution as a single tautomer. The 13C nmr spectroscopy shows that they are present in the triketo form in a number of polar and non-polar solvents. 2-Thiobarbituric acid derivatives, however, show extensive tautomerization. Their 13C chemical shift assignments were achieved by utilizing models 11a, 11c, 12b and 12d and from which relative tautomer
N-单和N,N-二烷基/二芳基巴比妥酸以单一互变异构体的形式存在于溶液中。的13 C NMR谱显示,它们存在于在许多极性和非极性溶剂的三酮形式。然而,2-硫代巴比妥酸衍生物显示出广泛的互变异构化。利用模型11a,11c,12b和12d实现了其13 C化学位移分配并据此确定相对互变异构体的分配比例。这些比率与各种溶剂的介电常数(ϵ)相关。硫代巴比妥酸还与具有羰基的溶剂形成加合物,只有具有硫酮或硫酚基的巴比妥酸酯才具有这种特征。6-氨基,6-甲基尿嘧啶和硫尿嘧啶以稳定的“烯”形式存在于DMSO溶液中,与乳清酸24及其硫代类似物25一样。化合物25在加热时或在溶液中长时间放置时会发生歧化和互变异构。关于“ 4,6-二羟基嘧啶”结构的文献矛盾,26,被解析,其互变异构体在溶液中由13 C nmr正确分配。