Characteristic Substituent-Shift Models for Carbon 1s Ionization Energies and Mean Dipole-Moment Derivatives

Abstract

Characteristic substituent-shift models for carbon mean dipole-moment derivatives are determined for the halomethanes, fluorochloroethanes, and some other small molecules. These models are analogous to those reported earlier for core ionization energies measured by X-ray photoelectron spectroscopy and are to be expected since Siegbahn's simple potential model relates these to mean dipole-moment derivatives obtained from infrared spectral data. Linear models relating carbon 1s ionization energies and mean dipole-moment derivatives to the number of fluorine, chlorine, bromine, and iodine atoms substituting hydrogen atoms in the halomethanes are reported. The regression coefficients in these models are similar to the coefficients for the fluorine and chlorine atoms found in linear models derived for the mean dipole-moment derivatives and carbon 1s ionization energies of the fluorochloroethanes. The signs of the coefficients in the fluorochloroethane model indicate that the R carbon becames more positive and the carbon more negative upon fluorine substitution for hydrogen. Standard derivative values of -0.52 ( 0.05, -0.25 ( 0.05, -0.18 ( 0.03, -0.17 ( 0.03, and -0.01 ( 0.01 e are proposed for the fluorine, chlorine, bromine, iodine, and hydrogen atoms of saturated fluorochlorohydrocarbons. Characteristic substituent shifts for Mulliken, CHELPG, and Bader charges of the carbon atoms in these molecules are also investigated.

Slater‐Like Model for Carbon 1s Core Ionization Energies of Halomethanes

“…Of course, relaxation effects also contribute to the experimental ionization energies but they are approximately constant for the halomethanes." Haiduke et al, [1] using his method to correlate with the carbon core electron ionization energies of some simple molecules (mainly compounds bearing one carbon atom), obtained an error of 0.31 eV, which is somewhat larger than the experimental errors of 0.1 eV. [1] In the study of the carbon 1s ionization energies, Thomas et al [3] considered that the ionization energies are affected by the electronegativity, hardness, charge distribution and relaxation, and moreover that the relaxation contributions increase with the size and polarizability of the halogens; his conclusions about the relaxation effect are somewhat in disagreement with those of Haiduke.…”

“…Haiduke et al, [1] using his method to correlate with the carbon core electron ionization energies of some simple molecules (mainly compounds bearing one carbon atom), obtained an error of 0.31 eV, which is somewhat larger than the experimental errors of 0.1 eV. [1] In the study of the carbon 1s ionization energies, Thomas et al [3] considered that the ionization energies are affected by the electronegativity, hardness, charge distribution and relaxation, and moreover that the relaxation contributions increase with the size and polarizability of the halogens; his conclusions about the relaxation effect are somewhat in disagreement with those of Haiduke. Moreover, Thomas et al [3] employed a multivariate second-order polynomial to relate the carbon 1s ionization energies of halomethanes, and obtained a good correlation expression, using which the calculating precision is within the experimental uncertainties.…”

“…[1] Since the atomic core ionization energy can provide information about the electronic density in specific regions of molecules, it is often used for the evaluation of the reactivity of molecular-specific regions of a compound. Indeed, the experimental core ionization energy can also be applied to test whether a theoretical calculation approach is correct or not, to verify the agreement between the theoretical hypothesis of a model and the practical molecular characteristics, to explain the effect of a substituent in a molecule on its inner electronic structure, and so on.…”

“…Siegbahn et al [2] first proposed a simple potential model, in which the core ionization energies are a function of the atomic charges and internuclear distances. Recently, Haiduke et al [1] developed Siegbahn's model into a function of mean dipole-moment derivatives of the nucleus being ionized and the other nuclei in the molecule (the mean dipole-moment derivatives were obtained from infrared spectral properties), and suggested that "Electronic density distributions close to the nucleus are prominent in determining both these quantities. Of course, relaxation effects also contribute to the experimental ionization energies but they are approximately constant for the halomethanes."…”

Determination of Carbon 1s Core Ionization Energies in Saturated Molecules

“…They are often used to evaluate the reactivity of specific molecular regions, and to investigate the information of molecular electronic structure changes and the effect of substituent on the atomic core ionization energy [1]. For example, Jolly [2 -4] used core electron ionization energy for the comparison of valence-shell ionization potentials and the quantification of the bonding and antibonding character of molecular orbitals.…”