Applications Of Electronic Effect In Estimating Energy Properties For Unconjugated Organic Compounds

The substituent electronic effects play a very important part in substituent effects of organic chemistry. It is crucial to understand and interpret the structure-property relationship. Thus, many chemists aspire to quantify its contribution.As important physical parameters, energy properties of organic compounds (such as enthalpies of formation, bond dissociation energies, ionization potential, et al) are closely related to some crucial thermodynamic and kinetic parameters, and have been widely applied in understanding, predicting and interpreting the properties change of organic compounds. These properties have been hotspots in theoretical chemistry reaserch. However, due to the limitation of experimental condition, it is impossible to determine the data of each enegy property for all compounds. Thus, it is still of significance to estimate energy properties data by theoretical method.In this thesis, a systematic research was made on some important theoretical issues about substituent electronic effects:A valence electrons equilibration method, which is used in calculating molecular electronegativity, group electronegativity, and atomic charge, is constructed; the change regularity of ionization potential for polyhalogenated hydrocarbons is investigated, and the weakest bound potential electron conception is proposed; on the basis of the experimental enthalpies of formation values of monosubstituted straight-chain alkanes, a novel method is defined to compute the intramolecular interactions between the substituent and an alkyl, with which the interaction potential index of16kinds of substituents are calculated; the contributions of intramolecular interactions between substituent Y, alkyl R1and alkyl R2are quantified respectively, and a theoretical model for estimating enthalpies of formation of R1-Y-R2is presented. Based on the above theoretical models and methods, energy properties of some unconjugated system are investigated:the ionization potential of alkanes and monosubstituted alkanes are eastimated; the ionization potential of polyhalogenated hydrocarbons are computed; the enthalpies of formation and bond dissociation energies of monosubstituted alkanes are estimated, and enthalpies of formation values for over2000monosubstituted alkanes are predicted; the enthalpies of formation of R1-Y-R2are estimated. This thesis involves four aspects as bellow:(1) Different from the traditional methods, we take the contribution of all valence electrons into consideration, and propose the new valence electrons equilibration method to calculate the equalized electronegativity. The molecular electronegativity (χve,m), group electronegativity (χve,G) and atomic charge (ΔNvc) are calculated and used to estimate the ionization potential of alkanes and monosubstituted alkanes, the chemical shift of1H-NMR, and the gas phase proton affinity of aliphatic amines, alcohols and ethers. All the expressions have good correlations. Moreover the Sanderson method and Bratsch method were modified on the basis of the valence electrons equilibration theory. The modified Sanderson method and modified Bratsch method are more effective than their original methods to estimate properties mentioned above.(2) The ionization potential of the polyhalogenated hydrocarbons has been studied theoretically by empirical method and quantum chemistry method, respectively. At first, we estimate the ionization potential of the polyhalogenated methanes by two empirical methods. The obtained results indicate the model IP=aχve+bPEIfi+c (χve is molecular electronegativity calculated by valence electrons equilibration method, and PEIfi is the influence of polarizability effect) based on the weakest bound potential electron method is reasonable and effective to predict the ionization potential for polyhalogenated methanes. Besides, the MOPAC AM1method and DFT (B3LYP) method were employed to calculate those ionization potential values. It is found the weakest bound potential method has more advantages. Furthermore, the experimental values of sixty seven polyhalogenated hydrocarbons were correlated with the parameters χve and PEIfi. The regression results show a good correlation (R=0.988), and the average absolute error between the experimental values and the calculated values is only0.10eV within the experimental uncertainties.(3) The interaction potential index IPI(X) of16kinds of substituents X (X=OH, SH, NH2, Br, Cl, I, NO2, CN, CHO, COOH, CH3, CH=CH2, C=CH, Ph, COCH3, COOCH3) were proposed, which are derived from the experimental enthalpies of formation ΔfH°(g) values of monosubstituted straight-chain alkanes. Based on the IPI(X) and polarizability effect index, a simple and effective model was constructed to estimate the ΔfH°(g) values of monosubstituted alkanes RX (including the branched derivatives). The present model takes into account not only the contributions of the alkyl R and the substituent X, but also the contribution of the interaction between R and X. Its stability and prediction ability was confirmed by the results of leave-one-out (LOO) method (rcv=0.9998, scv=3.4kJ/mol). Compared with previous reported studies, the obtained equation can be used to estimate enthalpies of formation for much more kinds of monosubstituted alkanes with less parameter. Thus, it is recommended for the calculation of the ΔfH°(g) for the RX.(4) The contribution of intramolecular interactions between substituent Y, alkyl R1and alkyl R2to the enthalpies of formation ΔfH°of R1-Y-R2were divided into three parts:the interaction of YR1and R2(φ[R2]φ[YR1]), the interaction of YR2and R1((p[R1]φ[YR2]), and the interaction of R1and R2(ψ[R1]ψ[R2]). The empirical model for estimating the ΔfH°of the monoderivatives of hydrocarbons RX, ΔfH°(RX)=h[R]+h[X]+φ[R]φ[X], was modified as the following model to calculate the ΔfH°of the R1-Y-R2, ΔfH°(R1-Y-R2)=h[R1]+h[R2]+h[Y]+φ[R1]φ[YR2]+φ[R2]φ[YR1]+ψ[R1]ψ[R2]. The Interaction Potential Index IPI(X) proposed in our resent work was used to expressed the intrinsic interaction of subsitituent Y on an alkyl, and a general expression for estimating the ΔfH°(g) of the secondary amines, ethers, thioether, and ketones were established. The obtained correlation results (r=0.9994, s=3.5kJ/mol, n=54) indicated that the expression are effective. The present method is proved to be as accurate as G3and G3MP2model chemistries in calculating the ΔfH°. Furthermore, it has specific physical meaning, and avoids bothersome calculations.