有机化合物电子光谱中的助色基及其作用机理探讨(Ⅱ)

助色基的未成键电子对与生色基的最低π~*反键轨道和最高π成键轨道线性组合成三个新的分子轨道。其中能量最高的π~*是反键轨道,它的能量一定高于原生色基的π~*轨道;最高占据π轨道的能级与原生色基的π轨道相比,孰高孰低将随生色基和助色基的不同而异;原生色基的n轨道与助色基的未共用电子对所占轨道相互正交,故两者间的作用可忽略不计,n轨道能级基本保持不变。因此助色基使生色基的n→π~*跃迁吸收波长发生蓝移,而π→π~*跃迁吸收波长是红移还是蓝移,则随生色基及助色基的不同而异。

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

The interaction between the p orbit of the auxochrome, the maximum bonding orbit (pi) and the minimum antibonding orbit (pi*) of the chromophore forms three new molecular orbit, among which the antibonding orbit (pi*') has the highest energy that is higher than those of the original pi*. The maximum occupied orbit (pi') will have energy lower or higher than those of pi according to different auxochrome and chromophore, and the energy of n orbit will remain steady, because the n orbit of the original chromophore is perpendicular to the p orbit of the auxochrome and the interaction is negligeable. As a result, the absorption wavelength of transition n-->pi* will shift towards higher photon energy, but for transition pi-->pi*, the absorption wavelength will shift towards either lower or higher photon energy, depending on the species of auxochrome and chromophore.