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关于芳香结构问题,从有机结构理论建立时起,就开始为人们所重视。根据苯及其衍生物所具有的特性,把当时的有机化合物划分为脂肪族及芳香族二大类。并且把这些特性用芳香性这个术语来概括,古典芳香性概念是指: (1)在合成过程中容易形成这种稳定的芳香环。 (2)具有特殊的稳定性,不易发生加成反应。 (3)容易发生亲电取代反应(硝化、磺化、卤代、傅克反应等)。 (4)某些取代基因为与芳香环连接表现出特殊的性质(如羟基呈酸性,胺基碱性的降低,卤素活性的降低,重氮化合物稳定性的增加等)。除了含有苯核的芳香族化合物以外,还发现吡啶、噻吩、呋喃、吡咯等杂环也具有芳香性。但是古典的芳香性概念是不够严格的,例如:萘比苯容易发生亲电取代反应,但稳定性却比苯差,同样对吡咯、呋喃等均有
On the issue of aromatic structure, from the time when the organic structure theory was established, people began to pay attention to it. According to the characteristics of benzene and its derivatives, the organic compounds were divided into aliphatic and aromatic two categories. And these properties are summarized in terms of aromaticity, which refers to: (1) This stable aromatic ring is easily formed during the synthesis. (2) has a special stability, less prone to addition reaction. (3) prone to electrophilic substitution reaction (nitration, sulfonation, halogenation, Friens reaction, etc.). (4) Some of the substitutions show special properties (such as acidic hydroxyl, decrease of basicity of amine, decrease of halogen activity, increase of stability of diazo compound, etc.) due to the connection with aromatic ring. In addition to benzene nuclei containing aromatic compounds, it was also found that pyridine, thiophene, furan, pyrrole and other heterocycles also have aromatic properties. However, the classical concept of aromaticity is not strict enough. For example, naphthalene is susceptible to electrophilic substitution, but its stability is worse than that of benzene.