The 1H and 13C n.m.r. rules for the assignment of 1, 3- and 1, 5- disubstituted pyrazoles: a revision
作者:Marta Bruix、Javier De Mendoza、Jose Elguero
DOI:10.1016/s0040-4020(01)86908-8
日期:1987.1
The H-5 signal of N-substituted pyrazoles is not shifted to low field values on increasing solvent polarity when a nitrogen lone pair lies very close to the measured proton (H-bond). Typical examples of this “abnormal” behaviour are provided by C,N'-linked, pyrazole-containing heterocyclic dimers. On the contrary, models selected in the 1,1'-bipyrazole and 2,2'biindazole series (N,N'-linkage) showed
当氮孤对非常靠近测得的质子(氢键)时,随着溶剂极性的增加,N-取代的吡唑的H-5信号不会移至低场值。这种“异常”行为的典型例子是由C,N'连接的含吡唑的杂环二聚体提供的。相反,在1,1'-联吡唑和2,2'-联吲唑系列(N,N'-键)中选择的模型由于其在NN键周围的非共面构象而显示出正常的位移。为了分配双取代的吡唑,建议使用质子耦合的13 C nmr光谱作为替代方法。