结构决定性质,性质是结构的体现,二者的辩证关系在有机教学中普遍存在。本文从电子效应、空间构型、空间位阻等现象试论结构与性质的辩证关系。 一、电子效应对物质性质的影响。 不同羰基化合物进行亲核加成反应的难易程度不同,举醛酮来说,醛比酮活泼,醛比较容易发生亲核加成反应,而酮则困难。这是性质上的差异,可以从结构上找到根据。因为羰基加成反应历程是属于亲核加成反应,羰基碳原子上电子云密度越低,就越容易发生亲核加成反应。相反羰基碳上的电子云密度越高,越不容易发生亲核加成反应,从结构上看,醛分子中的羰基碳只与一个斥电子烃基相连(甲基除外),而酮分子中羰基碳与两斥电子烃基相连,故醛分子中羰基碳的电子云密度比酮分子中羰基碳的电子云密度低,因此,醛的亲核加成反应的活性比酮高,所以在一般情况下,醛 Structure determines the nature and nature is the embodiment of the structure. The dialectical relationship between the two exists in organic teaching. This article discusses the dialectical relationship between structure and nature from the phenomena of electronic effects, spatial configuration, and spatial hindrance. First, the impact of electronic effects on the nature of the material. Different carbonyl compounds have different degrees of difficulty in nucleophilic addition reactions. In aldehydes and ketones, aldehydes are more active than ketones, aldehydes are more prone to nucleophilic addition reactions, and ketones are more difficult. This is a qualitative difference and can be found on the basis of structure. Because the carbonyl addition reaction process belongs to the nucleophilic addition reaction, the lower the density of the electron cloud on the carbonyl carbon atom, the more easily the nucleophilic addition reaction occurs. On the contrary, the higher the density of the electron cloud on the carbonyl carbon, the less nucleophilic addition reaction is likely to occur. From the structural point of view, the carbonyl carbon in the aldehyde molecule is connected to only one electron-repellent hydrocarbon group (excluding methyl groups), while the carbonyl group in the ketone molecule Carbon is connected to two repulsive electrons, so the electron cloud density of the carbonyl carbon in the aldehyde molecule is lower than the electron cloud density of the carbonyl carbon in the ketone molecule. Therefore, the activity of the nucleophilic addition reaction of the aldehyde is higher than that of the ketone, so under normal circumstances, ,aldehyde