Topological effect on MO energies,IV. The total π-electron energy ofS- andT-isomers

A novel general property of theS- andT-isomers (a concept which has been introduced and elaborated elsewhere^{1, 2}) of alternant hydrocarbons is demonstrated, namely that due to the HMO total -electron energy theS-isomer should always be more stable than theT-isomer. Some other classes of conjugated isomers are also constructed, for which similar inequalities are derived.

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Topologischer Effekt bei MO-Energien, 4. Mitt.: Die -Elektronen-Gesamtenergie vonS- undT-Isomeren

Zusammenfassung Es wird allgemein gezeigt, daß bei einemS-T-Isomerenpaar (beschrieben in^{1, 2}) eines alternierenden Kohlenwasserstoffes infolge der HMO -Elektronen-Gesamtenergie dasS-Isomere stets stabiler sein sollte als dasT-Isomere. Weitere Klassen konjugierter Isomere werden konstruiert und ähnliche Ungleichungen angegeben.

     

Ab initio MO calculation of hydration energies of ammonium ions and their solvation effect

The hydration energies for the NH⁺₄ and CH₃NH⁺₃ ions were calculated by an ab initio MO method. The aqueous solvation energy difference between these two ions was found to be accounted for by the interactions of the ions with a few solvent molecules.     

Determination of approximate bond dissociation energies by a semi-empirical MO technique

It is suggested that the Extended Hückel Method by Hoffmann may be used for the determination of approximate bond dissociation energies.The author would like to express his sincere gratitude to Miss Etta Rosenzweig for her assistance in this project.     

DFT and MO calculations of atomic and molecular chemisorption energies on surface cluster models

Summary Density functional theory (DFT) (including gradient corrections) and MCPF calculations have been performed for atomic (H, C, N, O) and molecular CH _x (x = 1–3) chemisorption on cluster models of different sites of the Cu(100) surface. The DFT and MCPF results are in good agreement once the important effects of core-valence correlation have been accounted for in the MCPF calculations by including contributions from a core polarization potential (CPP); in the DFT approach the core-valence correlation is obtained directly from the total density using the functional. Very large effects on the four-fold hollow site binding energy from core-valence correlation are found for C, N and CH. Several different DFT functionals were employed and compared in the calculations.     

Ab initio MO calculations on binding energies and stabilities of Na+ with ethylene diamine

Binding energies and stabilities of Na⁺ with bidentate ethylene diamine were studied using ab initio MO calculations with a 6-31G^* basis set. The computed results for bidentate ethylene diamine were compared with those for two (monodentate) CH₃NH₂ molecules.     

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.

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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.

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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.

     

On the advantages of hydrocarbon radical stabilization energies based on R-H bond dissociation energies

Hydrocarbon radical stabilization energy (RSE) estimates based on the differences in R-H vs CH(3)-H bond dissociation energies have inherent advantages over RSEs based on R-CH(3) vs CH(3)-CH(3), as well as R-R vs CH(3)-CH(3) comparisons, since the R-CH(3) and R-R reference systems are prone to unbalanced contaminating intramolecular interactions involving the R groups. When the effects of steric crowding, branching, protobranching, conjugation, and hyperconjugation are taken into account, R-CH(3) and R-R based RSE values are nearly identical to R-H RSEs. Corrections for electronegativity differences between H and R are not needed to achieve agreement.     

An mo study of the substituent effect in benzene radical ions

The effect of various types of substituents (X=OH, CH₃, CN, SiH₃) in benzene radical cations and anions have been investigated using INDO-SCF computations with and without π conjugation admitted between the substituent and the adjacent substrate. The inductive effect of the substituent has been found to play a minor role in determining the more stable configuration, the latter being determined in all cases investigated by the π conjugative interactions. A OEMO analysis of such interactions provides a better understanding of the key factors controlling the configuration preferentially stabilized in the various cases.     

On the calculation of surface energies

A simple formalism based on response theory is used to evaluate expressions for the surface energy of a uniform dielectric or metallic medium and the change in surface energy of a dielectric solvent when a dilute electrolyte is dissolved in it. The latter result coincides with the result of Onsager and Samaras.     

On the calculation of Auger energies

“Frozen-orbital” expressions within an average-energy formalism are presented for the calculation of Auger transition energies based on the orbitals determined for the initial state. Trial calculations at the minimal-basis level are reported for the K-LL transition in Ne, Na and Mg. We also discuss an ambiguity in the use of certain models for the calculation of both semi-empirical and ab initio Auguer energies. For illustration we give some numerical data on the atoms Ne, Na, Mg and S.     

SCF MO calculations of tropone,tropolone and related compounds

The variable-β procedure of the semiempirical SCF MO method was applied to tropone, tropolone and related compounds. Although the bond alternation in the heptagonal ring is neglected in the initial molecular geometry, the predicted transition energies show a good agreement with experiment, indicating the utility of this method for the calculation of the electronic spectra of non-benzenoid aromatic compounds. Discussions are given on the assignments of the absorption bands of tropone and tropolone.     

Topological effect on fluorescence emission of tetraphenylethylene-based metallacages

Herein, we describe the selective formation of a barrel-shaped or a ball-shaped fluorescent metallacage by controlling the shape and stoichiometry of the building blocks. Specifically, the tetraphenylethylenebased donor and two acceptors with different numbers of Pt(II) centers were combined via coordinationdriven self-assembly. Owing to the differences in the shapes of the assemblies, the resultant ball-shaped metallacage displayed stronger and blue-shifted fluorescence compared to the barrel-s...     

Mechanism of the photochemical reactions of substituted benzoquinones

Photoreactions of 2,6-dimethyl-, 2,6-di-tert-butyl-, and 2,6-diphenyl-1,4-benzoquinones with alcohols, organic acids, thioalcohols, amines (primary, secondary, and tertiary), cyclic ethers, tri- and tetraethoxysilanes are accompanied by the effect of chemical polarization of nuclei (CINDP) and lead, along with the formation of hydroquinones, to bicyclic and tricyclic structures and the products of radical substitution in the aromatic ring. The mechanisms of elementary photoreactions were elucidated. The intermediate excited states and radical structures were considered. For the first time permanent generation of radio waves in the course of the reversible photochemical reaction of substituted 1,4-benzoquinones with alcohols was detected.     

The effect of bond functions on dissociation energies

The procedure employing bond functions recently suggested by Wright and Buenker has been applied to the N₂ X ¹Σ_g⁺ potential curve within the CAS SCF+MRSD Ci treatment of electron correlation. The basis set used herein is identical to that employed by these authors in their SCF+CI calculations. The D_e and the shape of the resulting potential curve, as judged by the computed vibrational levels, is not so accurate as would be expected from the results reported by Wright and Buenker. Our results indicate that using the CI superposition errors associated with bond functions to cancel basis set incompleteness depends on the treatment of the electron correlation.     

Tempered orbital energies in SCF MO calculations and their relation to the ordinate in Mulliken-Walsh correlation diagrams and extended Hückel orbital energies

An “average state” of a molecule is defined by distributing the electrons equally among the valence orbitals of a minimal basis set Hartree-Fock calculation. The resulting eigenvalues, called tempered orbital energies, behave much more like the Mulliken-Walsh diagram energies or extended Hückel eigenvalues than do the Hartree-Fock canonical orbital energies.     

Effect of solvent nature on the photoreduction kinetics of substituted benzoquinones

Effect of the solvent nature on the kinetics of photoreduction of substituted benzoquinones in the presence of hydrogen donors has been studied. It has been found that the effective photoreduction rate constant (k_H) for quinones decreases with an increase in solvent polarity. For the 3,6-di-tert-butylbenzoquinone–1,2-N,N-dimethylaniline pair, the dependence of ln k_H on the difference of the reciprocals of optical and static solvent permitivities (1/ε _∞–1/ε₀) is stepwise with a break point corresponding to CH₂Cl₂. A similar relationship lnk_H = f(1/ε _∞–1/ε₀) is observed for the p-chloranil–mesitylene pair. In the study of the photoreduction kinetics for a series of seven o-benzoquinones in the presence of p-derivatives of N,N-dimethylaniline in CH₂Cl₂, it has been found that the dependence of k_H on the free energy of electron transfer (ΔG_e) has a maximum for the 3,6-di-tert-butylquinone-1,2–N,N-dimethylaniline pair at ΔG_e = 0.11 eV.