Triplet states via intermediate neglect of differential overlap: Benzene,pyridine and the diazines

The intermediate neglect of differential overlap technique is modified and applied to the calculation of excited triplet states. The resulting method generally reproduces the transition energies of the better-classified observations within a rms error of 1000 cm^–1. Trends are well reproduced, and the calculated orders ofn-* and -* triplet states are in good accord with the experimental information to date.The method is applied to benzene and the azines. The lowest four triplet states of benzene are calculated in good accord with experiment. Pyridine is calculated to have an-* triplet nearly degenerate with the lowest lying -* triplet, corroborating suggestions of Japar and Ramsay based on experimental information. A detailed analysis is made of the diazines, and assignments are suggested for the higher lying triplet states not yet classified or not yet observed.     

dπ-pπ interaction in bonds of silicon with nitrogen and phosphorus

Conclusions The stretching vibration frequencies of the Si-H bond in substituted silanes containing an Si-N bond depend both on the inductive effect of the substituents and the d-p, p,- and , -conjugation effects.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2609–2611, November, 1970.     

Calculation of some electronic excited states of formaldehyde

The optimized MO's of several excited states of formaldehyde have been calculated by means of a large basis set of modified Gaussian functions; particular attention has been paid to the * transition. The total energy of the various states has been obtained as the sum of the SCF and correlation energies; the last one has been calculated as a functional of the electronic density. The calculated values for the transition energies are in good agreement with the experiment. A strong interaction of the * state with the continuum is evidentiated; this fact can justify the absence of the * band in the absorption spectrum.     

Applications of the virtual charge model to the electronic structures and spectra of benzaldehyde and acetophenone

Summary The virtual charge model (Tapia model) in conjunction with the CNDO/S-CI approximation in the frame of SCF-MO theory was employed to study the effects of solvent on the electronic structures and spectra of benzaldehyde and acetophenone molecules. The CNDO/S calculations in presence of solvation indicate a satisfactory interpretation of the medium effects on the electronic structures and spectra of the molecules investigated. The prediction of our MO calculations by means of the Tapia model concerning the solvochromic shifts of n * and * transitions are in accord with the observed trends which indicate a blue shift for the n * band and a red shift for the * band upon a change of solvent from non-polar to polar solvents.

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Anwendung des Virtual Charge-Modells auf die Elektronenstrukturen und Spektren von Benzaldehyd und Acetophenon

Zusammenfassung Das Virtual-Charge-Modell (Tapia-Modell) im Zusammenhang mit der CNDO/S-CI-Näherung im Rahmen der SCF-MO-Theorie wurde zum Studium der Lösungsmitteleffekte auf die Elektronenstrukturen und Spektren von Benzaldehyd und Acetophenon herangezogen. Die CNDO/S-Rechnungen bei Anwesenheit von Solvens erlauben eine befriedigende Interpretation der Mediumeffekte auf Elektronenstrukturen und Spektren der untersuchten Verbindungen. Die aus MO-Rechnungen folgenden Voraussagen ergeben auf Basis des Tapia-Modells solvatochrome Verschiebungen für die n *- und *-Übergänge. Die vorausgesagten Effekte stehen im Einklang mit den experimentell beobachteten Trends: Blauverschiebung für die n *-Bande und Rotverschiebung für die *-Bande beim Wechsel von nichtpolarem zu polarem Lösungsmittel.

     

The Exciton Model and the Circular Dichroism of Polypeptides

Summary. Exciton coupling of the 190nm ^* transition is an important factor in the CD spectrum of peptides and proteins. The CD spectrum of the -helix is dominated by the exciton effect. The spectrum is sensitive to the direction of the ^* transition dipole moment, especially for short helices. Exciton theory is much less successful in accounting for the CD spectrum of the poly(proline)II (PPII) conformation, an important conformer in collagen and in unordered peptides. Mixing of the ^* transition with high-energy transitions in the peptide backbone and in side chains must be considered to explain the strong negative CD band near 200nm of PPII.     

Energy dissipation and selectivity in the catalytic oxidation of ammonia

A qualitative interpretation of selectivity changes in ammonia oxidation, based on considerations of energy dissipation processes is presented.

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Infrared spectra of vinyl compounds and the effects of conjugation involving the π-electrons of the vinyl group

Conclusions The frequencies of the =CH₂ group wagging vibration in CH₂=CH-X compounds reflects both the inductive effect of the substituents X, and the effects of, -, ,p- and (d-p)-conjugation in which these substituents take part.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No.l, pp. 152–154, January 1970.     

Calculation of σ→π* and π→σ* transitions in vinylboranes

Calculations are presented of the energies of the ground and excited and electronic states of ethylene and substituted vinylboranes. The Pople-Segal-Santry method was employed throughout. It is concluded that the excited state of lowest energy in ethylene has * character whilst the lowest energy ultra-violet spectral bands of the latter compounds stem from ^* transitions.

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Zusammenfassung Valenzelektronenrechnungen nach Pople-Segal-Santry wurden für Äthylen und Vinylborane durchgeführt. Danach hat der niedrigste angeregte Zustand von Äthylen ^*-Charakter, während die längstwellige UV-Bande der Vinylborane einem ^* -Übergang entspricht.

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Résumé Calculs de l'énergie pour les états fondamentaux et excités et de l'éthylène et des vinylboranes substitués. Utilisation de la méthode de Pople-Ségal-Santry. L'état excité le plus bas pour l'éthylène résulte d'une transition ^* , alors qu'il résulte d'une transition ^* pour les vinylboranes.

     

Allylation of π-benzeneruthenium bichloride with allyl compounds of mercury

Conclusions The reaction of-benzeneruthenium dichloride with the allyl compounds of mercury gave-benzene--allylruthenium halides that contain substituents in the-allyl group.Translated from Izvestiya Akademii Nauk SSSR, Moscow. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4. pp. 931–933, April, 1974.     

Calculations on the π→1π* transitions in large conjugated carbonyl compounds using the molecules-in-molecules method

Assignments of the ^1* electronic transitions in large carbonyl compounds have been carried out using the molecules-in-molecules method.     

Structure of 2,3- and 2,5-dihydroxypyridines

On the basis of an analysis of the UV and IR spectra, it was established that 2,3- and 2,5-dihydroxypyridines exist in different forms in neutral, acid, and alkaline media. The electronic absorption spectra of the neutral forms of the molecules and the distribution of the -electron charges in them were calculated by means of the Pariser—Parr—Pople (PPP) MO method. A comparison of the results of the calculations with the experimental UV spectroscopic data demonstrated that the calculations correctly predict the number of ^* absorption bands in the accessible region of the UV spectra and their positions and relative intensities.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 60–63, January, 1973.     

Charge-transfer complexes of indenophanes with π-acceptors

The charge-transfer (CT) spectra of the -complexes formed by a number of -acceptors with several indenophanes as well as indene as a model compound have been measured in methylene chloride at 20 °C. Association constants and transition energies of these complexes as well as ionization potentials of the -donors have been determined. The data obtained indicate the existence of transannular electronic interactions in the indenophane nucleus. Furthermore, the pseudo-para- andmeta[2.2]indenophane isomers (3 and4) show a large difference in their -base strength. A good linear relationship has been observed between the association constants and _max of the long wavelength CT bands for the -complexes of these -donors with both tetracyanoethylene (TCNE) and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ). All CT complexes studied have a 1:1 stoichiometry.

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Charge-transfer-Komplexe aus Indenophanen und -Akzeptoren

Zusammenfassung Die Charge-transfer-Spektren (CT-Spektren) von -Komplexen aus Indenophanen bzw. der Modellverbindung Inden und verschiedenen -Akzeptoren wurden in Methylenchlorid bei 20 °C bestimmt. Die Assoziationskonstanten und Übergangsenergien dieser Komplexe sowie die Ionisationspotentiale der -Donatoren wurden ermittelt. Die Daten sprechen für das Vorliegen transannularer elektronischer Wechselwirkungen im Indenophan-System. Die isomeren pseudo-para- und -meta[2.2]indenophane3 und4 unterscheiden sich in ihrer -Basizität deutlich. Es besteht eine gute lineare Korrelation zwischen den Assoziationskonstanten und _max der langwelligen CT-Banden der verschiedenen -Donatoren mit Tetracyanoethylen (TCNE) und 2,3-Dichlor-5,6-dicyano-p-benzochinon (DDQ). Alle untersuchten CT-Komplexe besitzen 1:1-Stöchiometrie.

     

Some peculiarities of π—π interactions between tetraphenylporphine metal complexes and aromatic solvents

The — complexes of metal tetraphenylporphinates with benzene, toluene, and xylenes were characterized by means of thermogravimetry. The ability of metalloporphyrins to form — complexes with certain -donor molecules depends largely on the -acceptor capacity of the macroheterocycle, and on the peculiarities of the metal—porphyrin coordinative linkage. Stoichiometry, energy parameters, and thermal stability of the - complexes of metalloporphyrins with various aromatic ligands are determined to a great extent by the molecular structure of solvents.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp.850–853, May, 1993.     

PPP and CNDO calculations for protonated molecules

CNDO calculations have been used to obtain the one-centre core integrals for protonated azines required in calculating the ^* absorption spectra of such molecules using the PPP method. Calculated spectra for both the parent and the protonated molecules are obtained in satisfactory agreement with experiment. The changes in the -framework of the molecules on protonation are also discussed in terms of the CNDO results.

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Zusammenfassung CNDO-Rechnungen wurden benutzt, um die Einzentren-Rumpf-Integrale für protonierte Azine zu erhalten, die bei der Berechnung der ^* -Absorptionsspektren mit Hilfe der PPP-Methode benötigt werden.Die berechneten Spektren für die Ausgangsmoleküle und die protonierten Moleküle sind in zufriedenstellender Übereinstimmung mit dem Experiment. Die Veränderungen im -Rumpf der Moleküle bei der Protonierung werden ebenfalls mit Hilfe der CNDO-Resultate diskutiert.

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Résumé Des CNDO ont tét utilisés pour obtenir les intégrales de coeur monocentriques des azines protonées nécessaires au calcul de leur spectre d'absorption ^* par la méthode PPP. Les spectres calculés pour les molécules protonées ou non sont en accord satisfaisant avec l'expérience. Les modifications subies lors de la protonation par le squelette sont discutées en fonction des résultats des calculs CNDO.

     

Study of the non-adiabatic transitions with application to NO

An expression for the non-adiabatic transition probability is derived from the viewpoint of the non-stationary character of the adiabatic approximation. A numerical calculation has been made for the free NO molecule. The non-adiabatic transition probability for the transition (B ² =0)(a ⁴ =9) is estimated to be 10^–6 sec^–1 by using the wave functions proposed by Moser et al.

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Zusammenfassung Für die nicht adiabatische Übergangswahrscheinlichkeit wurde aus dem nicht-stationären Charakter der adiabatischen Näherung ein Ausdruck hergeleitet, der für den Fall des NO-Moleküls numerisch ausgewertet wurde. Dabei ergab sich unter Verwendung der Wellenfunktionen von Moser u. Mitarb. eine Wahrscheinlichkeit für den Übergang (B ² =0) (a ⁴ =9) von der Größenordnung von 10^–6 sec^–1.

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Résumé Une expression pour la probabilité de la transition non adiabatique est obtenue du point de vue du caractère non stationnaire de l'approximation adiabatique. Un calcul numérique a été effectué pour la molécule NO isolée. La probabilité de transition non adiabatique pour la transition (B ² =0)(a ⁴ =9) est évaluée à 10^–6 sec^–1 en utilisant les fonctions d'onde proposées par Moser et al.

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This work was supported by The Faculty Grant of Arizona State University.     

Dipole moments and structure of the molecules of some oxazole derivatives

The values of the dipole moments of 15 substituted, 1, 3-oxazoles are given. The electron density distribution in the molecules of 2, 5-,2, 4-, and 4, 5-diphenyl-1, 3-oxazoles has been calculated by the LCAO MO method. Their heterocycle does not contain a single-electron system with the participation in conjugation of the-electrons of the C=N and C=C bonds and the p-electron pair of the oxygen. A vector calculation permits the detection of a considerable conjugation between substituents and the -electrons of the heterocycle through phenyl.     

Calculations of electronic spectra of Fe and Co porphyrins and their anionic forms

Energies and intensities of electronic transitions of a number of Co and Fe porphyrins and their anionic forms have been calculated by the INDO/S-CI method in the Zerner parametrization. The results from the theoretical analysis are consistent with the basic relationships observed in the change of electronic spectra within the limits of isoelectronic series of compounds characterized by identical total number of -electrons and identical filling of the pair of d orbitals. It has been established that in the spectra of compounds of an isoelectronic series corresponding to the neutral state of the porphyrin ligand, the allowed electronic transitions are described by superpositions of two ^* configurations (la_1u 4e_g) ) and (3a ^2u 4e_g ) , two configurations of intermolecular charge transfer 3 (d 2b_1u) and (d 3b_2u), and two types of doubly excited configurations (la_1u, d 4e_g, 4e_g) and (3a _2u, d 4e_g, 4e_g). Data have been obtained on the energies and orbital nature of the even electronic states that are responsible for rapid exchange of excitation energy of the porphyrin molecules with the transition metals.Leningrad. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 2, pp. 144–151, March–April, 1991. Original article submitted September 28, 1989.     

Hyperconjugation of unsymmetrical groups

The interaction of the -bond system with the -electron system in molecules of type {ie427-01} is easily determined for the symmetrical CH₃ group by isolating the -component from the system of three -bonds; CH₃ is thus treated as a C=X quasivinyl group. The theory is extended to unsymmetrical groups.Read at the Symposium on Quantum Chemistry, Palanga, June 1965.     

The inclusion of non-nearest neighbor ß terms in pariser-parr-pople type S.C.M.O. calculations

The calculation of -electron properties by an S.C.M.O. method including all _core terms has been extended to nitrogen and oxygen containing systems. The singlet ^* electronic transitions and -ionization potentials (where available) are in reasonable agreement with experiment. A comparison is made with the non-empirical all electron calculations of Clementi for pyrrole, pyridine and pyrazine.

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Zusammenfassung Die Berechnung von -Elektronen-Eigenschaften mittels einer SCMO-Methode, die alle _core-Terme einschließt, wurde auf Systeme mit Stickstoff- und Sauerstoffatomen ausgedehnt. Die Singulett- ^*-Übergänge und -Ionisierungsenergien sind in vernünftiger Übereinstimmung mit dem Experiment. Es wird einen Vergleich mit den nichtempirischen Rechnungen mit allen Elektronen von Clementi an Pyrrol, Pyridin und Pyrazin angestellt.

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Résumé Le calcul des propriétés des électrons par une méthode S.C.M.O. tenant compte de tous les termes _coeur a été étendu aux systèmes contenant de l'azote et de l'oxygène. Les transitions électroniques singulet ^* et les potentiels d'ionisation (lorsqu'ils sont connus) sont en accord raisonnable avec l'expérience. Les résultats sont comparés aux calculs non-empiriques de tous les électrons effectués par Clémenti pour le pyrrole, la pyridine et la pyrazine.

     

XPS and chemisorption studies of the surface layer of Pd?Ag catalysts for CO oxidation

XPS and chemisorption studies of the surface composition of a Pd–Ag alloy (5% Pd) before and after its application in CO oxidation have been performed. It is shown that in a freshly prepared sample the bulk and surface layer compositions are the same. High-temperature treatment of the catalyst in the reaction medium leads to a thermodynamic equilibrium between surface and bulk.

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Pd–Ag Pd 5% CO . , . .