MO LCAO calculations of the electronic spectra of the anions of 1,3-diketones with substituents at positions 1 and 3

The MO LCAO method is applied in the Hückel approximation to interpret the electronic spectra of the anions of 1,3-diketones having phenyl groups or double bonds in positions 1 and/or 3, as well as 1 and 2. It is found that one or two phenyl groups or double bonds in positions 1 and/or 3 produce a bathochromic shift in the strong NV₁ transition and the occurrence of a new fairly strong C₆H₅V₁ or C=CV₁ transition in the short-wave region. Simultaneous substituents in position 1 and 2 or 3 produce rather complex spectra, which are rather difficult to interpret by the simple MO LCAO method.     

MO LCAO calculations of the electronic spectra of the anions of 2-acyl-1, 3-diketones and certain other Β-diketones

The MO LCAO method (Hückel approximation) is used in an analysis of the electronic spectra of 2-acyl and 1-acyl-1, 3-diketones. It is found that the acyl group in the latter gives rise to a new electronic transition involving charge transfer to the acyl group. The effects of heteroatoms at positions 1 and 3 in the 1, 3-diketones are also examined.     

Polarographic reduction of 2-(4-pyridyl)indane-1,3-diones in dimethylformamide

The trend of the electrical reduction of isomeric 2-(4-pyridyl)indane-1,3-diones in dimethylformamide (DMF) was studied by classical and ac polarography, millicoulometry, ESR spectroscopy, and cyclical voltamperometry with a steady-state mercury electrode. The first reversible one-electron step leads to the formation of relatively stable anion radicals, which can be recorded by means of ESR spectroscopy. The corresponding dimers are detected in the course of prolonged electrolysis at a constant potential (at the level of the limiting current of the first wave). The second nonreversible step in the electrical reduction involves the indane-1,3-dionyl grouping and the pyridinium ring. Owing to their dipolar structure, the investigated compounds are reduced with considerably greater difficulty (by 400–550 mV) than the unsubstituted N-methylpyridinium salt.Translated from Geterotsiklicheskikh Soedinenii, No. 8, pp. 1097–1102, August, 1977.     

SCF MO CI calculations on the electronic spectra of fluorenone and related compounds

The electronic spectra of fluorenone, 9-iminofluorene and 9-ethylidenefluorene are studied by means of the SCF MO CI calculation. It is shown that the lowest singlet-singlet transition of fluorenone located at 380 m. can be assigned to a - ^* transition (¹ B ₂¹ A ₁). The nature and location of the lowest triplet state are also discussed.

---

Zusammenfassung Die Elektronenspektren von Fluorenon, 9-Iminofluoren und 9-Äthylidenfluoren werden mit Hilfe der SCF MO CI-Methode studiert. Es wird gezeigt, daß der niedrigste Sigulett-Singulett-Übergang in Fluorenon bei 380 m einem ^*-Übergang (¹ B ₂¹ A ₁) zugeordnet werden kann. Die Natur und Lage des niedrigsten Triplett-Übergangs werden ebenfalls studiert.

---

Résumé Les spectres électroniques de la fluorenone, du 9 iminofluorène et du 9-éthylidène fluorène sont étudiés à l'aide de calculs SCF-MO-CI. On montre que la plus basse transition singuletsingulet de la fluorénone, située à 380 m, peut être attribuée à une transition ^* (¹ B ₂¹ A ₁ La nature et la position du plus bas état triplet sont aussi étudiées.

     

SCF MO calculations of ultraviolet electronic spectra of azanaphtalenes with the variable Β approximation

The SCF MO method in the variable approximation has been applied to some azanaphtalenes. The transition energies and bond lengths of these molecules have been calculated. The results are in satisfactory agreement with experiment.

---

Zusammenfassung Das SCF-Verfahren wurde in Form der -Variationsmethode nach nishimoto und Forter auf einige Azanaphthaline angewendet. Die berechneten übergangsenergien und BindungslÄngen stimmen in befriedigender Weise mit dem Experiment überein.

---

Résumé Nous avons appliqué la méthode SCF MO dans l'approximation des variables à quelques azanaphtalènes et calculé les énergies de transition et les longueurs de liaison de ces molécules. Les résultats sont en accord satisfaisant avec l'expérience.

     

Allowance for polarization of atomic electron shells in MO LCAO calculations

The application of MO LCAO methods to molecules containing elements in the higher periods is discussed, especially compounds containing two phenyl rings linked via an oxygen atom. The calculated -electron density is found to agree with the observed electronic absorption spectra, dipole moment, effects of polarity on reactivity, and so on, provided that the wave function used for the heteroatom with n>2 is =c₁ npz+ +c_{2 nd}+...; the terms c_{2 nd}... provide correction for the change in the atomic function _npz produced by the surrounding atoms. This effect is not important for O, N, and C (first period). The effects of surrounding atoms on _npz for the halogen atom have evidently to be considered in computations on the -electron density for any molecule containing such an atom.     

All-electron SCF LCAO MO calculations on various conformations of cis- and trans-stilbene

Ab initio SCF calculations of cis- and trans-stilbene at different conformations were performed using two program systems. Minimal energy is obtained for cis-stilbene when the phenyl rings are rotated by 52 ° out of the molecular plane. The deviation from planarity due to steric hindrance is smaller for the trans isomer yielding a rotational angle of 19 °. The trans isomer is calculated to be more stable by 5.7 kcal/mole than the cis isomer, confirming the experimental estimate according to which the energy of isomerization is about 3 kcal/mole. This is an improvement over semiempirical calculations which predict a lower energy for the trans configuration.     

Study of the electronic structure and the spectra of methyl-substituted carbanions of nitrogen heterocycles by the selfconsistent field MO LCAO method

The -electron density distribution in the ground state and the energies of the spectral transitions were calculated by a semi-empirical version of the Pople-Pariser-Parr method for a number of carbanions derived from the removal of a proton from the methyl groups of toluene, isomeric methylnaphthalenes, methylpyridines, and benzoquinones. The results obtained are compared with the results obtained in a Hückel calculation of the same anions and with experimental data from the electronic spectra of methyl-substituted nitrogen heterocycles in a solution of potassium amide in liquid ammonia.The calculations reflect satisfactorily the characteristic features of the observed spectra. The effect of the choice of parameters for the self-consistent calculation is discussed and the contribution of singly or doubly excited configurations is explained.     

Photoelectron spectroscopy and ab initio LCAO MO SCF calculations on thiazyl fluoride

The He l, He II and Ne I photoelectron (p.e.) spectra of thiazyl fluoride. NSF, are compared with ab initio LCAO MO SCF calculations via Koopmans' theorem. The calculations predict the valence formulation NSF, and the p.e. spectrum is consistent with this. Comparisons are drawn with the isoelectronic molecule SO₂     

The use of Politzer's relationship in approximate MO LCAO calculations. I

Conclusion E II approximations in the MO LCAO method, constructed on the basis of Politzer's relationship between the components of the potential energy, are suitable for the approximate calculation of the total energies of molecules. The electron density distributions obtained are unsatisfactory. An attempt to correct the unsatisfactory features of versions I and IA is made in Paper II.Translated from Zhurnal Strukturnoi Khimii, Vol. 23, No. 1, pp. 3–9, January–February, 1982.     

Extended Fenske-Hall LCAO MO calculations of core-level shifts in solid P compounds

Extended Fenske-Hall LCAO-MO ΔSCF calculations on solids modelled as H-pseudoatom saturated clusters are reported. The computational results verify the experimentally obtained initial-state (effective atomic charges, Madelung potential) and relaxation-energy contributions to the XPS phosphorus core-level binding energy shifts measured in Na₃PO₃S, Na₃PO₄, Na₂PO₃F and NH₄PF₆ in reference to red phosphorus. It is shown that the different initial-state contributions observed in the studied phosphates are determined by local and nonlocal terms while the relaxation-energy contributions are mainly dependent on the nature of the nearest neighbors of the phosphorus atom.     

SCF LCAO MO calculations for the iso-electronic series ClO 4 − , SO 4 2− , and PO 4 3−

Ab initio SCF LCAO MO calculations have been performed for the ground states of the perchlorate, sulphate and phosphate ions. The basis sets used consisted of contracted gaussian-type orbitals having 12s, 10p and 2d-type primitive functions on the central atoms and 10s and 6p-type functions on the oxygens. The results are thought to be nearly at the Hartree-Fock limit.     

Electronic absorption spectra and protolysis of 4- and 5-azaindan-1,3-diones

The protolytic equilibria in a series of 2-aryl-substituted 4- and 5-azaindan-1,3-diones and the corresponding N-methylbetaines and 5,6-benzo analogs were studied by spectrophotometry. The substantial difference between the 4- and 5-aza derivatives is explained by the different effect of the anionic system on the Tr-electron density and the reactivities of the nitrogen atoms in the 4 and 5 positions. The protonation and deprotonation constants of the dipolar ions correlate linearly with the constants of the substituents in the 2-phenyl ring. In the case of 5,6-benzo-4-azaindan-1,3-diones, the keto group of the azaphthaloyl ring is protonated along with the dipolar ion in strongly acidic media.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1382–1386, October, 1972.     

Ab initio MO LCAO UHF calculations of the stability in dimeric ethylene radical ions

The stability of ethylene dimer ions has been computed by ab initio methods. The positively charged dimer is stable (0.6–0.7 eV) while the neutral and the negatively charged dimers are unstable with respect to decomposition into monomers. The magnetic hyperfine coupling constants have also been evaluated, hyperfine splittings are half those in the monomer in agreement with experimental data.     

Non empirical LCAO SCF MO investigations of electronic reorganizations accompanying core ionizations

Calculations have been carried out on an extensive series of molecules for both the neutral species and core ionized states. Substituent effects on C_1s , N_1s , O_1s , and F_1s levels have been investigated and where available comparison has been drawn with experiment. Comparison with Koopmans' theorem has allowed a relatively detailed study of change in relaxation energies as a function of substituent effect on a given core level. Whilst for C_1s levels the computed shifts in core binding energies are approximately linearly related to differences in relaxation energies for the N_1s , O_1s , and F_1s levels, the relative electronegativity of the substituent can invert this correlation. The empirical correction of Koopmans' theorem for differences in relaxation energies at different sites has been investigated for large molecules. The results compare well with direct hole state calculations.