【摘要】 本文讨论了共轭烯炔链物中反向端基的共轭效应。我们发现,凡是极化方向相同的单向基团,以任意组合直接相连,都没有体现共轭效应的π→π~*带或K带。当两个这样的单向基团同时连接于烯炔链的两端时,则其中有一个不包括在分子共轭基干以内。这种特殊的端基叫做反向端基。这种现象叫做反向端基效应。 反向端基效应可以用共轭极化或共轭位移的机理来解释。也可以从同系线性规律的专一性得到定性的阐明和定量的计算。反向端基系列电子吸收峰同系直线与相应不具反向端基系列的对比表明:反向端基的效应只相当于一个取代基,可以采用适当的反端基当量来表示。 本文中引入一种由基团诱导效应指数和共轭效应指数组成的反端基当量值S_n,将这种当量值代入同系直线方程式中,即得到下列关系其中N和S为通常的同系序数和代基当量总和,利用这个式子可以计算反向端基系列的电子吸收峰的波长,大多数计算值与实验值之差都在±5nm以内。更多还原

【Abstract】 In this paper the effect of opposite terminal groups in conjugated homologous series of polyenic and acetylenic compounds has been studied. We have found that any combination of two uni-directional conjugated terminal groups of the same type does not exhibit a π→π~* or K-band which is associated with conjugation. Furthermore, when two such uni-directional terminal groups are connected at both ends of an ethylenic or acetylenic chain, one of them does not participate in the conjugation with the chain. This particular type of terminal groups is designated here as opposite terminal groups, and their peculier structural effect which has been found to be a general phenomenon is termed the effect of opposite terminals.The existence of the effect of opposite terminal group can be readily explained by the conjugative mode of electronic displacement. It can also be demonstrated qualitatively by means of the uniqueness of the rule of homologous linearity, and its magnitude can be calculated with the aid of the equation of homologous linearity. A comparison of the homologous line for a series of compounds carrying an opposite terminal group with that of the corresponding series without such a group shows that the structural effect of an opposite terminal is equivalent only to that of a substituent instead of an ordinary terminal group, and that the effect of such an opposite terminal can be calculated by adopting a suitable equivalent for it.In this paper an opposite terminal equivalent S_a consisting of the inductive and the conjugative indices of the group concerned has been ??introduced When these equivalent values are substituted into the appropriate homologous linear equations, we have the following relationship where N and S are the usual serial number of homologs and the sum of the substitute equivalents, respectively. By means of this relationship the wavelengths of the electronic absorption peaks for different series with opposite terminal groups can be readily calculated. The main absorption peaks of about twenty such series including more than one hundred compounds are covered in this paper. Most of the calculated values are in agreement with experimental data within ±5nm.更多还原