Electronic Structure. Ionization Potential. Dipole Moment

4 Electronic Structure. Ionization Potential. Dipole Moment 

Electron Configuration. Electronic States. The NH ion is isoelectronic with the CH radical. Its ground state X 11 results from the ionization of the Iti MO in the NH(X 2 ) radical (cf. p. 31), and the lowest excited valence states arise from l7i- -3a, and 

4a 3a excitations. Experimentally observed are the ground state and the lowest four excited states with the following main electron configurations and dissociation limits [1]  

The ground state X has been identified with the lower, the states A, B, and C with the upper states of the three emission systems A- X, B- X, and C- X in the visible and UV region (cf. pp. 146/8). Perturbations of ground-state rotational-vibrational levels observed in the spectra were found to arise from strong interactions between the quasidegenerate X Ilr and a states. Rotational-vibrational transitions in the X and a states as well as between X and a have been observed in the IR (cf. p. 146). Term values of the excited states are listed together with the spectroscopic constants in Tables 5 and 6, pp. 140/2. 

The vertical excitation energies for the a A B A, C - X transitions at re = 1.9614 ao (the experimental value for the equilibrium internuclear distance in the NH molecule) were calculated by the many-body perturbation theory of second and third order (H study) [9]. 

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The specific properties studied here include charge distributions, energies, geometric structures and conformations, dipole moments, isomerization energies, bond dissociation energies, proton affinities, electron affinities, ionization potentials and spin populations, as well as the general trends in these and other properties, such as hypervalency character, and their underlying electronic structure causes. The comparison of calculated with experimental property values affords an opportunity to evaluate the computational methods. 

Various theoretical methods (self-consistent field molecular orbital (SCF-MO) modified neglect of diatomic overlap (MNDO), complete neglect of differential overlap (CNDO/2), intermediate neglect of differential overlap/screened approximation (INDO/S), and STO-3G ab initio) have been used to calculate the electron distribution, structural parameters, dipole moments, ionization potentials, and data relating to ultraviolet (UV), nuclear magnetic resonance (NMR), nuclear quadrupole resonance (NQR), photoelectron (PE), and microwave spectra of 1,3,4-oxadiazole and its derivatives <1984CHEC(6)427, 1996CHEC-II(4)268>. 

Quantitative structure-physical property relationships (QSPR). There are two types of physical properties we must consider ground state properties and properties which depend on the difference in energy between the ground state and an excited state. Examples of the former are bond lengths, bond angles and dipole moments. The latter include infrared, ultraviolet, nuclear magnetic resonance and other types of spectra, ionization potentials and electron affinities. 

Mulliken R. S. (1934). A new electroaffinity scale together with data on valence states and on valence ionization potentials and electron affinities. J. Chem. Phys., 2 782-793. Mulliken R. S. (1935). Electronic structure of molecules, XI Electroaffinity, molecular orbitals, and dipole moments. J. Chem. Phys., 3 573-591. 

Quantitative structure-activity relationships (QSARs) are important for predicting the oxidation potential of chemicals in Fenton s reaction system. To describe reactivity and physicochemical properties of the chemicals, five different molecular descriptors were applied. The dipole moment represents the polarity of a molecule and its effect on the reaction rates HOMo and LUMO approximate the ionization potential and electron affinities, respectively and the log P coefficient correlates the hydrophobicity, which can be an important factor relative to reactivity of substrates in aqueous media. Finally, the effect of the substituents on the reaction rates could be correlated with Hammett constants by Hammett s equation. 

Quantum mechanics is useful for calculating the values of ionization potentials, electron affinities, heats of formation and dipole moments and other physical properties of atoms and molecules. It can also be used to calculate the relative probabilities of finding electrons (the electron density) in a structure (Figure 5.8). This makes it possible to determine the most likely points at which... 

Aminothiazoles, chemical shift, proton, 68 coupling constants H-H, 74 dipole moment, 38 electronic structure, 44 ionization potential, 52, 83 substitution effects, 45 2-Aminothiazoles, antimicrobic and fungicidal properties of, 213 conversion into unsubstituted derivatives ... 

Quantitative structure-physical property relationships (QSPR). These involve infrared, ultraviolet, nuclear magnetic resonance and other types of spectra, bond lengths and bond angles, dipole moments, ionization potentials and electron affinities. 

The structural representation follows from the fact that the bond length between C-3 and C-4 is greater than that between C-2 and C-3 and between C-4 and C-5. The ionization potential is 8.89 eV, the electron being removed from the third r-MO (see Fig. 5.2b). The dipole moment is 0.71 D, with the negative end situated on the 0-atom. In contrast, the dipole moment of tetrahydrofiiran is 1.75 D. The small dipole moment of furan confirms that one electron pair of the 0-atom is included in the conjugated system and therefore delocalized. Furan has the following UV and NMR data ... 

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