Mechanism of phototransfer of hydrogen atom in the model H2CO + H2O system

A system modelling the photochemical abstraction of a hydrogen atom by ketones in alcohols is calculated by the semiempirical INDO and MINDO/3 methods with allowance for the configuration interaction in the singly and doubly excited states. The states participating in the elimination reaction and the electronic rearrangement taking place in the course of the reaction are traced on the basis of an analysis of the wave functions and the electron and spin densities. It is established that the state of the ketone which participates in hydrogen abstraction is a lowest triplet state of the n^* type, which is formed through the avoidance of intersections of several states of different orbital type ^3*, ³n^* and the charge-transfer state.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 476–480, July–August, 1989.     

Kinetics of oxidation of 2,2,4,5,5-pentamethyl-1-hydroxy-3-imidazoline-3-oxide by decanepersulfonic acid

The kinetics was studied of the oxidation of 2,2,4,5,5-pentamethyl-1-hydroxy-3-imidazoline-3-oxide by decanepersulfonic acid in a chloroform solution. The corresponding nitroxyl radical is quantitatively formed by the reaction 2=N-OH + RSO₄H 2=NO + RSO₃H + H₂O A mechanism of the reaction was proposed and the rate constant of the limiting stage of the process was determined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1265–1268, June, 1990.     

On the possibility of existence of η5-π-complexes of C60 fullerene: π-complexes with silicon

Qualitative estimates of possibility of the formation of fullerene ⁵--complexes have been carried out by the MNDO/PM3 method. It was shown, as exemplified by the C₆₀ cluster, that the introduction of five univalent functional groups R (R = H, Cl, Br) to -positions of a separate pentagon of C₆₀ with the formation of [R₅C₆₀]^– anions results in a pronounced increase in the -electron density on the atoms of this five-membered cycle and more favorable conditions for the formation of -bonds with the ⁵-ligand. The nature of the interaction between the atoms of the separate cycle in [R₅C₆₀]^– anion and ⁵-ligand was analyzed by the example of hypothetical sandwich systems R₅C₆₀SiCp. Half-sandwich complexes R₅C₆₀SiX (X = H, Cl) were also investigated. The local energy minima were found on the potential energy surfaces (PES) of systems R₅C₆₀SiCp and R₅C₆₀SiX with C_5p symmetry. These systems transform barrirlessly into q5-7E-complexes with the angular structure if the symmetry restrictions are removed. The most favorable conditions for ⁵--complexes of R₅C₆₀ to form are realized for R = H. The results obtained were compared to those of semiempirical and nonempirical calculations of bis (cyclopentadienyl) silicon.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2422–2429, October, 1996.     

Gamma resonance spectroscopic study of compounds containing the π-allylirontricarbonyl group

The gamma resonance (GR) spectra of a series of -allylirontricarbonyl compounds and -cyclopentadienyldicarbonyl complexes of iron have been recorded. The relationship between the GR spectra of these compounds and the electronic structure of the iron atom in the complexes has been examined. It has been shown that tetrahydrofuran, benzene, and acetonitrile do not react with -allylirontricarbonyl chloride, whereas dimethylformamide decomposes it with the formation of high-spin complexes of iron. The formation of the [-C₃H₅Fe(CO₃)]^– anion in the reduction of [C₃H₅Fe(CO₃)]I by naphthalene-sodium in benzene has been confirmed.     

Nature of the pentamethyldisilanyl group in organosilicon compounds

Summary The positige inductive effect of the pentamethyldisilanyl group (CH₃)₃SiSi(CH₃)₂ and the election-acceptor effect of its p-d bond with an aromatic ring are appreciably greater than the analogous effects of the trimethylsilyl group (CH_{3 3}Si, which gives ground for the postulation of the presence of a p-d-d¹ bond in the fragment C_sp ²-Si-Si.     

Metal complexes of allyl derivatives of C60 fullerene: molecular and electronic structure prediction from density functional calculations

The problem of existence of ³—-complexes of C₆₀ fullerene with transition metal atoms is discussed. The complexes C₆₀R₃Co(CO)₃ (R = H, F, Cl, Br), C₆₀H₃NiCp, and C₆₀H₃Fe(CO)Cp, where C₆₀R₃ is an allyl derivative of C₆₀ fullerene, were shown to be sufficiently stable. In these complexes the metal atoms are ³—-bound to the fullerene cage. In contrast to this, the metal atoms in the C₆₀H₃Li and C₆₀H₃FeCp complexes are ⁵—-coordinated to the carbon cage. Density functional calculations were carried out with the Perdew—Burke—Ernzerhof exchange-correlation potential (PBE). It was concluded that the type of bonding in the complexes of allyl derivatives of C₆₀ fullerene depends on the nature of the species attached. Among the systems studied, the maximum energy of the ³—-bond was obtained for the C₆₀H₃NiCp complex. The results obtained can be useful in the design of synthesis of new fullerene derivatives with the ³—-coordination of the transition metal atoms to the carbon cage.     

Synthesis of stable oxazolidine nitroxyl radicals with methoxy groups at the α-carbon atoms to the radical site

The condensation of -hydroxyaminoalcohols with aldehydes and acetone gave 3-hydroxyoxazolidines and tautomeric N-(2-hydroxyethyl)--arylnitrones, whose oxidation by PbO₂ in methanol leads to stable oxazolidine nitroxyl radicals with methoxy groups at C² and C⁴.Novosibirsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 966–973, April, 1992.     

Crystal Structure of Copper(II) and Cobalt(II) Hexafluoroacetylacetonate Complexes with 2,2,5,5-Tetramethyl-4-phenyl-3-imidazoline-1-oxyl-3-oxide

The crystal structures of the copper(II) and cobalt(II) hexafluoroacetylacetonate complexes with the nitroxide 2,2,5,5-tetramethyl-4-phenyl-3-imidazoline-1-oxyl-3-oxide (PhImOx) Cu(hfac)₂(PhImOx), Co(hfac)₂(PhImOx), and Co(hfac)₂(PhImOx)₂ have been determined. The former two are chain type complexes, whereas the latter has a molecular structure. The coordination polyhedra of the copper and cobalt atoms are tetragonally distorted octahedra. In the two chain type compounds, the octahedra are formed from the hfac anion, nitroxyl, and N-oxide O atoms; in the molecular complex, the O atoms of the NO groups are not coordinated to the metal atoms. In the structure of Cu(hfac)₂(PhImOx), F...F contacts equal to 2.805 have been found.     

13C and 29Si NMR spectra and intramolecular interactions in derivatives of phosphaalkenes R-P=C[Si(CH3)3]2

Analysis of the ¹³C, ²⁹Si, and ³¹P NMR spectra in the series of C-bis(trimethylsilyl)phosphaalkenes made it possible to differentiate between the mechanisms of the electronic effects of the substituents R at the P atom on the -system of the -P=C(SiMe₃)₂ group. It was established that substituents R capable of n (or ) conjugation (NMe₂, OR, Hlg) substantially perturb the -system, destabilizing the levels of the occupied MO of the P=C bond; substituents with poorly defined -donating (accepting) characteristics (tert-Bu, iso-Pr, CN, Ph) only influence the investigated system through its polarization. Criteria which agree with the reactivity characteristics of the phosphaalkenes were obtained.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 729–733, November–December, 1988.     

Proton-magnetic-resonance spectra of some organoethoxysilanes

The PMR spectra of 33 organoethoxysilanes have been investigated. Comparison of the chemical shifts of C₂H₅O and CH₃ groups attached to the silicon atom with the values of the remaining substituents at the central silicon atom gives reason to suppose that the contribution of each atom in p– interaction decreases with increased number of ethoxy groups at the silicon atom, while the over-all effect of increased electron density at the silicon heteroatom arising from this interaction increases. The Taft constants for several substituents are calculated.     

Spin density distribution in paramagnetic azafullerene

Hyperfine coupling (HFC) constants for ¹⁴N and ¹³C nuclei in azafullerene C₅₉N (1) were calculated. The HFC constants for the ¹H and ¹³C nuclei in the ^·CH₃ radical were calculated as functions of the pyramidal distortion of the angles at the carbon atom. Using this angular dependence, the spin density distribution of the unpaired -electron in 1 was determined. The spin density of the unpaired -electron in 1 is mainly localized around the nitrogen atom.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2372–2374, November, 2004.     

Polydentate coordination of the thallium atom in complexes with chiral amidinylcyclopentadienyl ligands

The chiral thallium amidinium cyclopentadiene-N-ylide complexes [C₅(CO₂Me)₄{ArNC(Ar")NAr}]Tl were synthesized and structurally characterized by X-ray diffraction analysis and NMR spectroscopy. In these complexes, an unusual mode of coordination of the thallium atom was found, viz., the thallium atom is coordinated by both the side-chain nitrogen atom (N—Tl, 2.833(6) ) and the system of the cyclopentadienyl ring (Tl—Cp, 2.887(4) ⁵-bonding).     

Complexation between N-allylmorpholinium derivatives and copper(I) halides. Synthesis and crystal structure of π-complex {[C4H8ONH(C3H5)]+}2[Cu2Cl4]2?

Copper(I) -complex {[C₄H₈ONH(C₃H₅)]⁺}₂[Cu₂Cl₄]^2– (I) was obtained by ac electrochemical synthesis from N-allylmorpholine hydrochloride and copper(II) chloride in ethanol and structurally characterized. In structure I, copper and chlorine atoms form unique noncentrosymmetric Cu₂Cl ₄ ^2– fragments. Both crystallographically independent N-allylmorpholinium cations are involved in the -interaction and are coordinated by the copper atom through the C=C bond of the allyl group. The trigonal pyramidal environment of the Cu(1) atom is composed of three chlorine atoms and the C=C bond, while the Cu(2) atom coordinates two chlorine atoms and the C=C bond forming a planar triangle. The extremely strong N-CCl hydrogen bond (HCl 2.2 ) prevents the Cl(1) atom from acting as a bridge and favors the formation of fragments Cu₂Cl ₄ ^2– .__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 4, 2005, pp. 306–310.Original Russian Text Copyright © 2005 by Goreshnik, Davydov, Myskiv.     

Structural Chemistry of Cu(I) Allyl and Acetylene π-Complexes

Stereospecific behavior of allyl derivatives and acetylenes in CuX -complexes (X = Cl^-, Br^-, NO₃ ^-, BF₄ ^-, 1/2SiF₆ ^2-, 1/2SO₄ ^2-) is studied by X-ray diffraction analysis. The influence of donor atoms N, S, and O and of the Cu-X bond polarization on the -complex formation is considered. The efficiency of Cu-(C=C) and Cu-(CC) -interaction and specific behavior of mono- and disubstituted acetylenes with respect to Cu(I) are compared.     

Thermodynamic parameters of free radical-dimer equilibria in phenylindandione derivatives

Conclusions Measurements of the thermodynamic parameters of the free radical-dimer equilibrium in benzene for 2,2-bis[R-2-(p-dimethylaminophenyl)indan-1,3-diones] with different substituants R on the phthaloyl ring have been carried out. The equilibrium constants satisfy the Hammett equation (p=0.87, benzene, 20C). The bond breaking energy of the central C₂–C₂' bond in the dimers amounts to 18–20 kcal/mole The extinction coefficients of the 2-aryl-indan-1,3-dione-2-yl radicals in benzene have been determined. The long-wave band of the radicals displays thermo- and solvatochromism.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1237–1243, June, 1988.     

Exohedral η5-π-complexes of fullerene C20

The problem of stabilization of polyhedral carbon clusters, which do not obey the isolated pentagon rule, is discussed taking a dodecahedral fullerene C₂₀ as an example. Ab initio MO LCAO calculations in the HF/3-21G approximation showed that fullerene C₂₀ as well as its C₂₀H₅ hydrides with C _5v symmetry can form stable 2⁵--complexes of the CpFeC₂₀FeCp and H₅C₂₀FeC₂₀H₅ types. The energies of the ⁵-Fe--C₂₀ -bonds in these complexes were compared with those of the Fe--Cp bond in ferrocene and the Fe--C₆₀ bond in the ⁵--C₆₀H₅FeCp complex.     

Conformational energy of the methy group at the C(5) atom in 1,3,2-oxazaborinates

The method of³H and¹³C NMR spectroscopy was utilized to determine the conformational energy of the methyl group at the C₍₅₎ atom in molecules of 2,3,5-substituted 1, 3, 2-oxazaborinanes. The resulting value of G⁰ (1 kcal/mole) is half the value of 1, 3, 2-dioxaborinanes and is close to the analogous value in tetrahydro-I, 3-oxazines (1.2 kcal/mole). The differences observed are associated with features of the p--electronic interactions in the heteroatomic fragment of the organoboron ring.     

A Nonempirical Quantum-Chemical Study and Natural Bond Orbital Analysis of C6H5XCY3 Species (X = SO or SO2, Y = H or F)

The potential functions of internal rotation about the C² _sp—S bonds for C₆H₅XCY₃ species (X = SO or SO₂, Y = H or F) have been obtained at the MP2 (full)/6-31+G(d) level of ab initio theory. It is found that the spatial structures with the plane of C² _sp—S—C³ _sp bonds, which is near perpendicular to the benzene ring plane, are the energy-favourable conformations. The values of the rotational barrier about the C² _sp—S bond are equal to (kJ/mole): 21.2 (C₆H₅SOCH₃), 29.0 (C₆H₅SOCF₃), 20.4 (C₆H₅SO₂CH₃), and 28.2 (C₆H₅SO₂CF₃). On the basis of the Natural Bond Orbital (NBO) analysis results, it has been revealed that the double S=O bond is a strongly polarized covalent -bond, whereas -bond electrons practically are localized on the oxygen atom. The S=O bond order for aromatic sulfoxides and sulphones is mainly caused by hyperconjugational interactions according to the LP(O) ^*(S—C_ipso) and LP(O) ^*(S—C _Y ) mechanisms. In sulphones there is also the additional mechanism of hyperconjugational interactions such as LP(O^{1 *}(S—O²) and LP(O²) ^*(S—O¹). With the replacement of one hydrogen atom on the —XCY₃ group, the charge loss of the unsubstituted benzene molecule increases: —SOCH₃ < —SO₂CH₃ < — SOCF₃ < —SO₂CF₃. The substitution of the —CH₃ group for the —CF₃ group weakly influences the charge value on the sulfur atom but effects the acceptor characteristics of the substituent to a greater extent than the variation of the sulfur atom coordination.