取代基效应定量研究新进展

综述了最近20多年有机化学取代基效应定量研究所取得的诸多新进展.主要内容包括：（1）电负性均衡原理得到普遍认同并用于计算分子中电荷分布和基团的诱导效应,分子电负性计算方法在几何平均法、调和平均法、加权平均法的基础上又提出了价电子均衡方法,进一步扩展了电负性均衡原理的应用范围.（2）试剂亲电、亲核能力的实验测定,提出了以二苯甲基正离子和醌甲基化合物等作为参考化合物的标定方法,其研究范围被扩展到气相条件、有机金属反应和自由基体系,得到一系列试剂的亲核参数N和亲电参数E.理论上提出亲电性指数和亲核性指数的概念及其定量计算公式,并对实验测定参数和理论计算指数之间的关系进行了深入研究.（3）极化效应参数从最初的经验方法,进而采用量子化学方法计算,再用统计方法提出了烷基极化效应指数PEI和基团极化效应参数PEIX,被广泛用于解释和估算有机化合物的气相酸碱性、电离能、生成焓、键能、反应速率、水溶解性和色谱保留值.（4）直接由取代苯的紫外光谱吸收能量计算得到的取代基激发态参数exCC,不同于取代基在分子处于基态的极性参数和自由基状态下的自旋离域效应参数,该参数用于对位二取代苯、取代二苯乙烯、二取代氮苄叉苯胺等多类有机化合物紫外光谱的定量相关,结果良好.（5）立体屏蔽效应的提出区分了传统的三种立体效应.在羰基与亲核试剂加成反应立体选择性定量表示,提出了立体选择性指数Ci;在表示基团对反应中心表面积屏蔽的定量提出了屏蔽参数SR,进一步基于反应中心体积被屏蔽的角度提出了拓扑立体效应指数TSEI,这些参数在分子内二面角、反应的立体选择性、烯烃和烷基苯的生成焓、咪唑离子液体的酸性以及烷烃与羟基自由基的反应速率等方面得到良好的应用.此外,论文还对有机化学取代基效应定量研究中值得进一步深入探索的领域和问题提出了建议和展望.

Recent progress of quantifying substituent effects

This paper summarizes significant progresses of quantifying organic substituent effects in recent 20 years.The main content including：（1） The principle of electronegativity equalization was widely accepted,and used to calculate the intramolecular charge distribution and inductive effect of groups.A valence electrons equilization method was proposed to compute the molecular electronegativity on the basis of geometric mean method,harmonic mean method,and weighted mean method.This new calculation method further extended the application of the principle of electronegativity equalization.（2） A scale method was established for experimentally determining the electrophilic and nucleophilic ability of reagents,in which benzhydryliumions and quinone methides were taken as the reference compounds,and the research field was extended to the gas phase conditions,organometallic reaction and radicals system.Moreover,the nucleophilicity parameters N and electrophilicity parameters E for a series of reagents were obtained.The definition and quantitative expression of electrophilicity index ω and nucleophilicity index ω were proposed theoretically,and the correlation between the parameters from experimental determination and the indexes from theoretical calculation was also deeply investigated.（3） The polarizability effect parameter was initially calculated by empirical method and further developed by quantum chemistry method.Recently,the polarizability effect index of alkyl （PEI） and groups （PEI X ） were proposed by statistical method,and got wide applications in explaining and estimating gas-phase acidity and basicity,ionization energy,enthalpy of formation,bond energy,reaction rate,water solubility and chromatographic retention for organic compounds.（4） The excited-state substituent constant ex CC ,which was obtained directly from the UV absorption energy data of substituted benzenes,is different from the polar constants in molecular ground state and the radical spindelocalization effects constants in molecular radical state.The proposed constant ex CC correlated well with the UV absorption energy of many kinds of organic compounds,such as 1,4-disubstituted benzenes,substituted stilbenes,and disubstituted N-benzylidenebenzenamine.（5） The presence of the steric shielding effect distinguished three traditional steric effects.The stereoselectivity index C i was proposed to quantify the stereoselectivity in addition reaction of carbonyl with nucleophilic reagent.The shielding parameter R S ′ was defined to quantitatively express the specific surface of the reaction center screened by a group.Further,the topological steric effect index （TSEI） of a group based on the relative specific volume of reaction center screened by the atoms of substituents was proposed.These parameters have good applications in estimating the intramolecular dihedral angles,stereoselectivity of reaction,enthalpies of formation of alkene and alkylbenzene,acidity of substitutedimidazolium ionic liquid,and the reaction rate of alkane and hydroxyl free radical.In addition,some suggestions and prospects for further studies on quantifying the organic substituent effects were presented in this paper.