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1.
A. N. Egorochkin Yu. D. Semchikov N. S. Vyazankin S. Ya. Khorshev 《Russian Chemical Bulletin》1970,19(1):143-145
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. 相似文献
2.
Robert W. Woody 《Monatshefte für Chemie / Chemical Monthly》2005,136(3):347-366
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. 相似文献
3.
Electron transitions in divinyl chalcogenides (CH2=CHXCH=CH2, where X is S, Se, or Te) have been analyzed using UV absorption spectra of dialkyl and alkyl vinyl chalcogenides. The following relations for the orbital energies are found: * < * < * < * for Te and * < * < * < * for S and Se. For chalcophenes, a correlation between the energy of the excited state (E
*) of specific symmetry, the ionization potential (I) and the electron affinity (EA) is obtained:E
*=const+(I+EA)/2. The electron affinity of divinyl chalcogenides is estimated. The correlation between the excited * states of divinyl chalcogenides and chalcophenes is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 831–835, May, 1994. 相似文献
4.
A. Jaumà A. Escuer J.-A. Farrera J. M. Ribó 《Monatshefte für Chemie / Chemical Monthly》1996,127(10):1051-1062
Summary Several Mn, Cu, and Zn chelates of etiobiliverdin-IV-, mesobiliverdin-IX, and its dimethyl ester are studied. The results show that the chemical constitution of the Cu biliverdin chelate corresponds to a formal metal oxidation state of (II) coordinated to a neutral radical of the NH trideprotonated biliverdin. The reactivity of the Cu(II) bilindione chelates in nucleophilic solvents agrees with that expected for a neutral radical structure of the ligand; in CH3OH, they undergo oxidation towards dimethoxybilipurpurins. The magnetic behaviour of Cu(II) etiobiliverdinate-IV- in the solid state shows an intramolecular weak antiferromagnetic coupling d9Cu-to--radical (J=–23 cm–1) and an intermolecular weak antiferromagnetic coupling -radical-to--radical (J=–45 cm–1). The analogy of this magnetic behaviour to that of the cation radical of metalloporphyrins is discussed.
Reaktivität von Pyrrolpigmenten, 21. Mitt.: Struktur und Reaktivität von Cu(II)- und Zn(II)-Chelaten von Bilindionen
Zusammenfassung Einige Mn, Cu and Zn Chelate von Etiobiliverdin-IV-, Mesobiliverdin-IX und seinem Dimethylester werden untersucht. Im Komplex koordiniert ein Metallatom (mit der Formalladung II) mit einem Neutralradikal des dreifach NH-deprotonierten Bilindions. Die Reaktivität des Komplexes gegenüber nukleophilen Lösungmitteln entspricht erwartungsgemäß dem eines neutralen -Radikals; in CH3OH wird er zu Dimethoxybilipurpurin oxidiert. Bei Cu(II)-Etiobiliverdinat-IV beobachtet man im festen Zustand neben schwacher, antiferromagnetischer Kupplung zwischen d9Cu und -Radikal (J=–23 cm–1) auch eine schwache, intermolekulare, antiferromagnetische Wechselwirkung zwischen zwei -Radikalen (J=–45 cm–1). Dieses magnetische Verhalten wird dem des -Kationradikals von Metalloporphyrinen gegenübergestellt.相似文献
5.
J. S. Kwiatkowski 《Theoretical chemistry accounts》1970,16(3):243-246
The electronic absorption spectra (
* type) of the mixture of the enolic and zwitterionic forms of both 3-hydroxypyridine and 5-hydroxypyrimidine are interpreted by means of the Pariser-Parr-Pople type calculations. 相似文献
6.
An extention is reported of a previously proposed semiempirical approach based on geminal functions and formulas are given for the transition moments and the electronic population analysis.The case of pyridine is considered as an example and used to predict the n
* or
* character of its lower transition.This work was carried out with the financial support of the Consiglio Nazionale delle Ricerche (C.N.R.), Roma. 相似文献
7.
A theoretical investigation is made of the electronic states ofp-benzoquinone (PBQ), methyl substituted PBQ's and 1,4-naphthoquinone (NQ). In accord with experiment, the lowest triplet state of PBQ is calculated to be3
B
1g
(n, *), while that for duroquinone (DQ) is3
B
3g
(, *). The electron densities of these states are consistent with the hypothesis that3
n, * states lead to oxetan formation and3, * states to cyclobutanes. It is predicted that trimethyl PBQ might form both adducts, as the two states are calculated to be nearly degenerate.The photochemistry of NQ is more complex. The lowest excited triplet state is calculated to be ofn, * symmetry, in accord with experiment; however, several other states are predicted near in energy, and the photochemistry cannot be rationalized unambiguously.This work was supported in part by the National Research Council of Canada. 相似文献
8.
L. I. Savranskii 《Chemistry of Heterocyclic Compounds》1972,8(4):473-476
The -electron structures and spectra corresponding to singlet -singlet - transitions of neutral and protonated pyridyl- and quinolylamine molecules were calculated by the MO LCAO method within the semiempirical Pariser-Parr-Pople approximation with allowance for configuration interaction. It is shown that the -electron density distribution explains the different directions of nucleophilic and electrophilic substitution reactions in the neutral and protonated heterocycle molecules. It is concluded that the character of protonation of amino-substituted quinolines is distinct.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 520–524, April, 1972. 相似文献
9.
Sizova O. V. Ershov A. Yu. Ivanova N. V. Shashko A. D. Kuteikina-Teplyakova A. V. 《Russian Journal of Coordination Chemistry》2003,29(7):494-500
A number of complexes were synthesized with the general formula cis-[Ru(Bipy)2(L)(Cl)](BF4), where Bipy is 2,2"-bipyridine, L is pyridyne (Py), 4-aminopyridine (4-NH2py), 4-picoline (4-Mepy), nicotin-amide (3-CONH2py), isonicotinamide (4-CONH2py), 3- and 4-cyanopyridine (3-CNpy, 4-CNpy), 4,4"-bipyridine (4,4"-Bipy), trans-1,2-bis(4-pyridyl)ethylene (Bpe), 4,4"-azopyridine (Azpy), pyrazine (Pyz), imidazole (Imid), and NH3. The semiempirical CINDO-CI method was used to calculate the energies and intensities of transitions in the electronic absorption spectra. The differences observed in the spectra of these compounds are mainly due to the positions of the charge-transfer transitions d
(Ru) *(L). Depending on the positions of these transitions, ligands L can be divided into three groups: 1) transitions Ru L lie in the region of the first long-wavelength band d
(Ru) *(Bipy) (L = Azpy, Pyz); 2) transitions Ru L lie between the first and second bands due to the charge transfer to Bipy (L = 3-CONH2py, 4-CONH2py, 4,4"-Bipy, Bpe, 4-CNpy), and 3) transitions Ru L lie in the region of the second band d
(Ru) *(Bipy) (L = Py, 4-Mepy, 3-CNPy, 4-NH2py, Imid). 相似文献
10.
Richard W. Bigelow Hans-Joachim Freund Bernhard Dick 《Theoretical chemistry accounts》1983,63(3):177-194
The nature of the lowest energy triplet state (T
1) ofp-nitroaniline (PNA), N,N-dimethyl-p-nitroaniline (DMPNA) and nitrobenzene (NB) is reexamined using the semiempirical CNDO/S-CI method with selected parameter options. The present results indicate that in the case of theunperturbed molecules the short-axis polarized * n() triplet largely localized at the acceptor end of the molecule may lie lower in energy than the triplet manifold counterpart of the intense intramolecular charge-transferD
+ A
–singlet excitation. Computations suggest, however, that polar solvents strongly stabilize the PNA and DMPNA * charge-transfer triplet relative to other excitations, whereas specific solvent hydrogen-bonded interactions stabilize the * n() triplet of NB below those of * character. These assignments allow a rationalization of phosphorescence lifetime data,T
n
T
1 absorption measurements and relative photochemical behavior. 相似文献
11.
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.
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.
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.相似文献
12.
A. E. Lutskii A. V. Shepel O. P. Shvaika N. P. Demchenko G. P. Klimisha 《Chemistry of Heterocyclic Compounds》1970,4(2):268-271
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. 相似文献
13.
Lei Liu Wen-Guang Li Qing-Xiang Guo 《Journal of inclusion phenomena and macrocyclic chemistry》1999,34(4):413-419
A multiple regression model was generated, which can satisfactorily estimate the association constants (K
a
) for the inclusion complexation of -cyclodextrin with mono- and 1,4-disubstituted benzenes. It was found that lnK K
a
was correlated with the substituent molar refraction (R
m
), hydrophobic constant () and Hammett constant ) of the guest compounds with a correlation coefficient of 0.95. The main driving forces for -cyclodextrin complexation was concluded to consist of van der Waals forces and hydrophobic interactions, while the influence of electronic effects was small. 相似文献
14.
Warren T. Zemke 《Theoretical chemistry accounts》1971,22(1):23-38
The low-lying states of H2 consist of one core () and one valence () electron and afford a direct evaluation of intershell - interaction. After resolution of the electronic energy into only, only, and - parts, it is shown that an electronic change in this model system is due solely to a change in the electrons. Simple Hückel theory is examined. If the molecular core is represented properly, regardless of the wave function the calculated and parameters are in reasonable agreement with the empirical parameters. This agreement appears to be due to a fortuitous cancellation of energy contributions.
Work performed in part under the auspices of the U.S. Atomic Energy Commission.
Work aided by the U.S. Public Health Service via grant GM 08068. 相似文献
Zusammenfassung Die niedrig liegenden -Zustände des H2 bestehen aus einem Rumpfelektron und einem Valenzelektron und ermöglichen eine direkte Auswertung der --Wechselwirkung zwischen zwei Schalen. Nach der Zerlegung der elektronischen Energie in -,- und --Anteile wird gezeigt, daß eine elektronische Veränderung in diesem Modellsystem nur auf eine Veränderung des -Elektronenanteils zurückgeht. Die einfache Hückeltheorie wird untersucht. Wenn der Molekülrumpf geeignet dargestellt wird, so sind, unabhängig von der -Wellenfunktion, die berechneten Parameter und in guter Übereinstimmung mit den empirischen Parametern. Diese Übereinstimmung scheint auf eine starke Auslöschung von Energieanteilen zurückzugehen.
Résumé Les états inférieurs de H2 consistent en un électron de coeur () et un électron de valence () et fournissent une évaluation directe de l'interaction entre couches -. Après expression de l'énergie électronique en parties , et -, on montre qu'une modification électronique de ce système modèle est due seulement à une modification des électrons . La théorie de Hückel simple est examinée. Si le coeur moléculaire est convenablement représenté, quelle que soit la fonction d'onde , les paramètres at calculés sont en accord raisonnable avec les paramètres empiriques. Cet accord apparaît comme le résultat d'une compensation fortuite de contributions énergétiques.
Work performed in part under the auspices of the U.S. Atomic Energy Commission.
Work aided by the U.S. Public Health Service via grant GM 08068. 相似文献
15.
I. M. Skvortsov L. N. Astakhova S. N. Kuz'min I. Ya. Evtushenko 《Chemistry of Heterocyclic Compounds》1978,14(3):293-297
Reduction of 5-[2-(methoxycarbonyl)ethyl]-1,3-dihydropyrrolizines with lithium aluminum hydride gave 5-(-hydroxypropyl)-1,2-dihydropyrrolizines (in 70–90% yields), which have intramolecular -hydrogen bonds in dilute solutions. The parameters of the -hydrogen bonds were determined in the IR spectra, and their enthalpies were found. The data obtained (OH 95–99 cm–1, –H 3.05 kJ·mole–1) show that among compounds with an aliphatic hydroxyl group and a system of electrons, 5-(-hydroxypropyl)-1,2-dihydropyrrolizines have some of the strongest intramolecular -hydrogen bonds.See [1] for communication XVI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 359–363, March, 1978. 相似文献
16.
Summary A quantitative treatment, coupled with critical qualitative considerations, pertaining to the study of thermodynamics of adsorption of N2 and CO2 on different graphite samples, through the evaluation of the film pressure, as a function of temperature and pressure, is presented. The . determination of the adsorbent specific surface areas is affected through the graphic manipulation of the Langmuir adsorption equation utilizing data adopted from literature, and the values are then computed by employing the Gibbs adsorption equation by making use of the areas under them-lnP curves. The results deduced are discussed specifically in terms of as related to the nature of the adsorbents, the magnitude of the calculated thermodynamic functions and the specific surface areas for the individual adsorbents.
Zusammenfassung Die Arbeit bringt eine thermodynamische Studie der Adsorption von N2 and CO2 an verschiedenen Graphitpräparaten. Grundlage der Betrachtung ist der Filmdruck als Funktion der Temperatur und des Druckes. Die Bestimmung der spezifischen Oberfläche des Adsorbens wird beeinflußt durch die graphische Behandlung der Langmuirschen Adsorptionsgleichung. Es wurden Literaturwerte adoptiert und-Werte nach der Gibbsschen Adsorptionsgleichung berechnet. Die abgeleiteten Ergebnisse werden diskutiert und zur Natur des Adsorbens, zur Größenordnung der berechneten thermodynamischen Funktionen und zur spezifischen Oberfläche der einzelnen Adsorbentien in Beziehung gesetzt.相似文献
17.
Second order perturbation theory is used to calculate the energy lowering due to all and double excitations on the ground state, and of all and double and triple excitations on the first excited singlets. The values obtained are compared to previous results coming from configuration interaction calculations including all single and some double excitations. The computations are carried out on CNDO/2 and Del Bene-Jaffé wavefunctions.
Zusammenfassung Mit Hilfe der Störungstheorie zweiter Ordnung wird die Energieerniedrigung berechnet, die durch Einschluß aller - und -Doppelanregungen auf den Grundzustand, sowie durch Berücksichtigung aller doppelten und dreifachen - und -Anregungen auf die ersten angeregten Singuletzustände bewirkt wird. Die so erhaltenen Werte werden mit Ergebnissen früherer CI-Rechnungen, die unter Berücksichtigung aller einfachen und einiger doppelter Anregungen erhalten wurden, verglichen. Die Berechnungen werden mit CNDO/2- und Del Bene-Jaffé-Wellenfunktionen durchgeführt.
Résumé On utilise une méthode de perturbation au deuxième ordre pour calculer l'abaissement d'énergie dû à l'interaction de toutes les configurations diexcitées ( et ) sur l'état fondamental, et à l'interaction de toutes les configurations di- et triexcitées ( et ) sur les premiers états excités. Les valeurs obtenues sont comparées aux résultats antérieurs de l'interaction de configuration incluant les états monoexcités et certains diexcités. Les calculs sont effectués sur des fonctions d'onde de type CNDO et Del Bene-Jaffé.相似文献
18.
The cis-influence observed in chlorine NQR data of X, Y affecting the Pt-Cl bonds in compounds of type trans-[PtCl2XY] is interpreted. -bonding differences in Pt-Cl bonds are suggested to account for the trends in NQR frequencies. Pt-Cl -bonding is negligibly small for both d
(Pt)–p
(Cl) and p
–p
(Cl) interactions. 相似文献
19.
Conclusions The effects of d-p and, conjugation in the vinyl and allyl derivatives of silicon and germanium depend on the nature of the other three substituents.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2074–2076, September, 1971. 相似文献
20.
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. 相似文献