This paper summarizes significant progress in quantifying organic substituent effects in the last 20 years. The main content is as follows： （1） The principle of electronegativity equalization has gained wide acceptance, and has been used to calculate the intramolecular charge distribution and inductive effect of groups. A valence electrons equalization 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 electro- philicity parameters E for a series of reagents were obtained. The definition and quantitative expression of electrophilicity in- dex co and nucleophilicity index co were proposed theoretically, and the correlation between the parameters from experimental determination and the indexes from theoretical calculation was also investigated. （3） The polarizability effect parameter was initially calculated by empirical method and further developed by quantum chemistry method. Recently, the polarizability ef- fect index of alkyl （PEI） and groups （PEIx） 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 Crcc obtained directly from the UV absorption energy data of substituted benzenes, is different from the polar constants in molecular ground state and the radical spin-del
In this paper,Topological Electronegativity Index (TEI) was developed to express the relatively power of an group in a molecule to attract electrons to itself.The charge effect,the relaxation effect and the electrostatic field effect on the C 1s core ionization energies of saturated molecules were evaluated,based on the topological electronegativity index TEI,the atomic electronegativity χP and the polarizability α.The charge effect was scaled by the topological electronegativity index discrepancy between the C and X (X is atom or group) in the C-X bond.The relaxation effect (induced dipole) was scaled by the charge on the ionized carbon atom together with the polarizabiliy of the X.The electrostatic field effect was scaled by the charges on the atoms attached directly to the ionized carbon atom.Further,the shielding effect ΔSi of the C 1s electron in the saturated molecules was expressed by the charge effect and the relaxation effect together with the electrostatic field effect.By introducing the ΔSi into the Slater model,a Slater-like model was obtained for calculating the C 1s core ionization energy E1,C of saturated molecules,whose correlation coefficient r is 0.99943 and the average absolute error between the calculated and the experimental C 1s core ionization energies is only 0.094eV for 81 saturated molecules.Also the cross-correlation was tested by the leave-one-out (LOO) cross-validation method,and the obtained model has good predictive ability and stability (the correlation coefficient rcv is 0.99928,the average absolute error between the predicted and the experimental values is only 0.105 eV).
A correlation equation between the UV absorption wavenumbers of 1,4-disubstituted benzenes and the excited-state substituent constant was obtained. For 80 sorts of 1,4- disubstituted benzenes, the correlation coefficient was 0.9805, and the standard deviation was only 672.27 cm^-1. The results imply that the excited-state substituent constant can be used productively for research on UV energy of 1,4-disubstituted benzenes. The present method provides a new avenue to study the UV absorption spectra of aromatic systems with the excited-state substituent constant, and it is helpful to understand the effect of substituent electrostatic effects on the chemical and physical properties of conjugated compounds with multiple substituents in excited state.
