The substituent effect (SE) is one of the most important topics in organic chemistry and related fields, and Hammett constants (σ) are commonly used to describe it. The results of the computational studies carried out for Y–R–X systems (reaction sites Y = NO₂, O^–; substituents X = NO₂, CN, Cl, H, OH, NH₂; spacers R = polyene, polyyne, acene with n = 1–5 repeatable units) show that the substituent properties depend significantly on n, the type of R, and Y. Results of the analysis of the substituent effect stabilization energy and geometrical parameters of the Y–R–X systems reveal that (i) the SE strength and its inductive and resonance components decay with the increase in spacer length, its weakening depends on the Y and R type; quantitative relations describing decay are presented; (ii) the ratio between inductive and resonance effect strength changes with n and depends on Y; (iii) differences in the substituents’ properties are examples of reverse SE; (iv) in general, structural parameters are mutually well correlated as well as with the SE descriptors; (v) due to the strong O^– resonance effect, the changes in π-electron delocalization within R are well correlated with the SE strength only for Y = O^– systems.

中文翻译：

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从能量学和分子几何角度看并苯、多烯和多炔衍生物中的取代基效应

取代基效应（SE）是有机化学及相关领域最重要的课题之一，常用哈米特常数（σ）来描述它。Y-R-X 体系的计算研究结果（反应位点 Y = NO ₂、O ^–；取代基 X = NO ₂、CN、Cl、H、OH、NH ₂；间隔基 R = 多烯、多炔，n = 1-5 个可重复单元的并苯）表明取代基特性很大程度上取决于nY-R-X系统的取代基效应稳定能和几何参数的分析结果表明，（i）SE强度及其感应和谐振分量随着间隔基的增加而衰减长度，其削弱取决于Y和R类型；提出了描述衰变的定量关系；(ii) 感应效应强度与谐振效应强度之比随n变化并取决于 Y；(iii) 取代基性质的差异是反向 SE 的例子；(iv) 一般而言，结构参数以及与 SE 描述符相互之间具有良好的相关性；(v) 由于强烈的O-^共振效应，仅当Y = O时，R内π电子离域的变化与SE强度有很好的相关性^–系统。