有机化合物电子光谱中的助色基及其作用机理探讨(Ⅰ)

本文就电子光谱中助色基的作用进行了讨论 ,认为不能一概地认为助色基能使与之相连的生色基最大吸收波长统统发生红移 ,而应具体问题具体分析 :对于n→π 来说 ,一方面助色基的p轨道和生色基的最低π 反键空轨道相互作用 ,使π 反键轨道能量上升 ,另一方面助色基的p轨道和生色基的n轨道正交 ,n轨道能量基本保持不变 ,因此n→π 跃迁能增加 ,吸收波长发生蓝移。对于π→π 跃迁来说 ,助色基的p轨道和生色基的最高π成键轨道相互作用生成的新的最高π成键轨道 ,能量虽然有所升高 ,但升高的程度与π 反键轨道升高的程度相比 ,在一些化合物中π轨道升高程度较大 ,因而π→π 跃迁能减小 ,吸收波长发生红移 ;在另一些化合物中π轨道升高程度较小 ,因而π→π 跃迁能增加 ,吸收波长发生蓝移。

Study on the Auxochrome of the Electronic Spectrum of Organic Compounds and Its Effect Mechanism(Ⅰ)

This paper discusses the effect mechanism of auxochrome of electronic spectrum. The study proves that the auxochrome does not invariably make the maximum absorption wavelength of chromophore shift towards lower photon energy. For the transition of n-->pi*, the p orbit of the auxochrome interacts with the minimum antibonding empty orbit(pi*), which will make the energy of pi* increase, while the p orbit of the auxochrome is perpendicular to the n orbit of chromophore, and the energy of the n orbit will remain steady ultimately, so the transition energy of n-->pi* will increase. For the transition of pi-->pi*, the interaction of p orbit of the auxochrome and maximum bonding orbit (pi) of the chromophore forms new orbits, so the energy of the maximum bonding orbit in new orbits will increase. In some compounds, the increase is higher than those of pi*, so the transition energy of pi-->pi* will decrease and absorption wavelength will shift towards lower photon energy, which, however, is reverse in other compounds.