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在有机化学中,酮式——烯醇式互变异构是较普遍和重要的异构现象之一。一般地说,结构上类似于乙酰乙酸乙酯的化合物部不同程度存在这种变异构现象。这种互变异构由倾向主要取决于α—氢原子的酸性,即取决于pKa的大小。本文讨论了pKa的含义。介绍了测定有机化合物pKa的方法,从一些化合物的pKa大小与烯醇式含量的关系,定量说明了烯醇式含量随化合物pKa减小而升高,即酸性越强,烯醇式含量越高,並从理论上解释了这一现象,而这个问题在许多有机化学参考书中还没有作具体、祥细的讨论。 酮式—烯醇式互变异构现象的重要内容之一。例如,早年对乙酰乙酸乙酯结构的研究中发现了它能与羟氨、苯肼等羰基试剂作用;能与亚硫酸氢钠作用生成白色结晶状加成物;能与氢氰酸作用生成β—氰基—β—羟基酸。这些实验依据充分明了乙酰乙酸乙酯具有酮式结构。
In organic chemistry, keto-enol tautomerization is one of the more common and important isomerism. In general, the compound structure is similar to the ethyl acetoacetate to varying degrees, the existence of this variant phenomenon. The tendency of this tautomerism depends mainly on the acidity of the α-hydrogen atom, ie on the size of pKa. This article discusses the meaning of pKa. The method for the determination of pKa in organic compounds was introduced. The relationship between the pKa of some compounds and the content of enol was quantitatively explained. The enol content of pKa decreased with the decrease of pKa, that is, the stronger the acidity, the higher the enol content , And explain this phenomenon theoretically, and this issue has not been discussed in detail in many organic chemistry reference books. One of the important contents of keto-enol tautomerism. For example, early studies on the structure of ethyl acetoacetate found that it can with hydroxylamine, phenylhydrazine and other carbonyl reagents; with sodium bisulfite to generate white crystalline adduct; with hydrocyanic acid generated β Cyano-β-hydroxy acids. The experimental evidence is well understood that ethyl acetoacetate has a keto structure.