Orbital interactions in anti- and syn- tricyclooctadienes and their homoderivatives

Photoelectron spectroscopy and molecular orbital calculations of the Extended Hückel, MINDO/3 and STO-3G Hartree-Fock type have been applied to anti- and syn-tricyclo[4.2.0.0^2,5]octadiene (1 and 2) and their homo and bishomo derivatives. The resulting ordering of the one-electron levels for 1 and 2 are 7a _g ( ₊), [6b _u (), 5b _u (_–)], 4a _u (), 3a _u () and 7a ₁(₊), 5b ₂(), 6b ₂(_–), 3a ₂(), 4b ₁(), respectively. The present results differ substantially from those previously published.     

Quantum-chemical study of allylic compounds with two bonded heavy atoms

It has been shown by the CNDO method that the bathochromic shift of the long-wave absorption band in the transition from allylstannane to compounds of the type C=C-C-Sn-X and C=C-Sn-X (where X is a heavy atom) is connected with the formation of a low-energy vacant *_S-X orbital, localized mainly in the region of the Sn-X chemical bond, and of an occupied _Sn-X orbital, the energy of which is somewhat higher than of the _C-Sn orbital. The dependence of the position of the long-wave absorbance region on conformation is related to the fact that, in planar and nonplanar conformers, the long-wave transitions are of a different type ( * and *, respectively); the bathochromic shift is determined to a large degree by the difference in the energies of the highest occupied MO ( - ) in the s-trans form. In the nonplanar conformers the heavy atom orbitals interact with the -orbital of the ethylene moiety through the bridge group; this leads to a significant delocalization of the HOMO and to a considerable change in its energy. On the other hand, their interaction with the *-orbital in compounds of the C=C-C-Sn-X type is very low and does not favor the delocalization of lower vacant MO. In vinyldistannane the *-orbital is noticeably delocalized, due to the interaction with the *_Sn-Sn orbital in planar and with the *_Sn-Sn orbital in nonplanar conformers.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 636–641, March, 1992.     

Charge control in the formation of complexes of phenol with unsaturated compounds containing organometallic substituents from group IV

The resonance donor effect of the , conjugation of R₃M and R₃MCH₂ (M = Si, Ge, Sn; R is an alklyl group) substituents with the triple bond in compounds R₃MC=CX and R₃MCH₂CCX (X = H, R) changes on passing from isolated molecules to their H-complexes. A partial ⁺ charge on the triple bond enhances , conjugation; a partial ^– charge on the triple bond has practically no effect on the resonance properties of R₃M substituents, whereas the , conjugation of R₃MCH₂ substituents diminishes owing to the effect of negative direct resonance interaction. The effect of , conjugation on the effective negative charges of the carbon atoms in the -CC- fragments was estimated quantitatively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1041–1046, June, 1994.This work was supported by the Russian Fundation for Basic Research (Grant 93-03-18372).     

Inclusion of dynamic σ-π polarization in π-electronab initio calculations

Summary A method is presented, whereby dynamic - polarization, i.e. the correlation effect expressed by simultaneous (-*, -*) excitations, can be approximately included in a multi-reference configuration interaction (MRCI) or multi-configurational self-consistent field (MC-SCF) calculation, without need to explicitly correlate the sigma orbitals. The method, which we call the capacitance matrix method, is based on the use of conventional one-electron integrals, from which a polarization potential (SPP) contribution is computed and added to the one- and two-electron Hamiltonian. In the present form, the method requires one parameter for each type of atom, and one for each type of bond. These parameters were adjusted to reproduce the dynamic - polarization energy, computed by restricted multi-reference CI calculations, of a number of states of different hydrocarbons, and the agreement was within a few percent. Using the same parameters in CAS (Complete Active Space) SCF calculations of various states of benzene gives excitation energies, when SPP is included, which is comparable to those obtained by much more elaborate MRCI calculations.     

Reactions of 1,2,4-Triazines with Nucleophiles. 6. Use of SNH Methodology for the Direct Introduction of Cyclic Diketone Residue into the 1,2,4-Triazine Ring FORENAME = D. N.

3-R-6-Phenyl-1,2,4-triazine 4-oxides react with cyclic -diketones (dimethylbarbituric acid, dimedone, and indan) in both acidic (substrate activation) and basic conditions (nucleophile activation) with formation of ^H-adducts, intermediates in the nucleophilic substitution of hydrogen (S_N ^H) in 3-R-5-Nu-4-hydroxy-6-phenyl-4,5-dihydro-1,2,4-triazines. Oxidative aromatisation of these intermediates or auto-aromatisation of acylated (benzoyl chloride) at the NOH -adducts with elimination of benzoic acid gave the corresponding substituted 1,2,4-triazine 4-oxides or 1,2,4-triazines.     

Structure and vibrational spectra of dicyclopentadienylzinc. A DFT study

The quantum-chemical DFT calculations of the Cp₂Zn structure confirm the conclusion made earlier from the vibrational spectra that the sandwich structure (⁵-C₅H₅)₂Zn (A) is not energetically favorable and more favorable are the close in energy -structure (⁵-C₅H₅)(¹-C₅H₅)Zn (B) and -structure (¹-C₅H₅)₂Zn (C). The vibrational spectra of structures B and C with the DFT-derived force fields were calculated. A comparison of the calculated spectra of the isolated Cp₂Zn molecules with the experimental data gives no way of deciding between the B and C structures. It is most likely that the molecule is nonrigid and experiences a strong influence from the nearest environment in solution or in the crystalline state.     

The electronic structure of molecules by a many-body approach

The vertical valence ionization potentials of cyclopropane, ethylene oxide and ethylene imine are calculated by a many-body Green's function method. For C₃H₆ the ordering of the ionization potentials is 2e(), 1e(), 2a₁(), 1a₂(), 1e(). The assignment of the 2a₁ and the 1a₂ ionization potentials which has been controversial is thus clarified. The ordering is in agreement with the result obtained via Koopmans' theorem. For ethylene oxide and ethylene imine Koopmans' theorem fails in predicting the correct order of ionic states. For C₂H₄O the ordering of the ionization potentials is 2b ₁(), 4a ₁, 1a ₂(), 2b ₂,3a ₁, 1b ₁(), 1b ₂, 2a ₁ and for C₂H₅N 6a, 5a, 3a, 2a, 4a, 3a, 1a, 2a. The agreement of the computed ionization potentials with the experimental values is very satisfactory.     

Regioselectivity in the reactions of the acetonate ion with electron-deficient arenes

The reactions of the acetonate ion with 1,3-dinitro-5-X-, 1,3-X₂-5-nitro- (X = NO₂, CN, COOCH₃, CONH₂, COO^–, and H), and 1,3,5-tricyanobenzenes were studied by ¹H NMR and electronic absorption spectroscopy and by quantum-chemical methods. The kinetic factor is decisive for the initial attack of the carbanion on the C(2) atom of unsymmetrical arenes. However, -adducts in which a nucleophile is added to the C(4) atom are more stable thermodynamically. In the case of 1,3-X₂-5-nitrobenzenes (X = CN, COOCH₃, or CONH₂), the -adducts with the acetonate group in para-position to the X group unexpectedly proved to be very stable. The structures of the -adducts based on trinitro- and 1,3-dinitro-5-cyanobenzenes were determined by X-ray diffraction analysis. Quantum-chemical calculations (the AM1 and PM3 semiempirical methods and the density functional method) were used to interpret the reaction regioselectivity and the molecular and electronic structures of the -adducts.     

Diatomic interactions in momentum space. The 2pπ u and 3dπ g states of H 2 + system

The recently proposed method of momentum electron density for interatomic interactions is applied to the two states of the H ₂ ⁺ system. The processes of the attractive 2P _u and repulsive 3d _g interactions are analysed based on the behaviour of the momentum density and Compton profile. The results are compared with the previous ones for the 1 _{S g} and 2p _u states. The guiding principle of contraction and expansion for the energy-density relation in momentum space is shown to be common to both the and states.     

Stable σ-adducts of 4,6-dinitrotetrazolo[1,5-a]pyridine with alkoxide anions

The reaction of 2-chloro-3,5-dinitropyridine with two equivalents of KN₃ in the presence of ROH results in stable Meisenheimer-type -adducts of 4,6-dinitrotetra-zolo[1,5-a]pyridine with RO^– anions (R = H, Alk, Ph). The mechanism of -complex formation was suggested. The structure of the -adduct with R = Me was established by IR and NMR spectroscopy and by X-ray diffraction analysis.For the preliminary communication, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1278–1283, July, 1994.This work was supported by the Russian Foundation for Basic Research (project code 93-03-5329).     

Temperature deactivation of excited Tb3+ in the presence of 1,2-dioxetane in acetonitrile

Quenching the fluorescence (FL) of terbium perchlorate by 2,2-adamantane-2,2-dioxide (1) was shown to have a chemical character and was caused by the formation of the [1...Tb³⁺] complex. The dependence of the lifetime () of FL of Tb^*3+ in acetonitrile on the temperature and concentration of1 has been studied. The temperature dependence of is caused by a rearrangement of the inner sphere of the aquasolvate complexes of Tb³⁺, which leads to the replacement of H₂O with MeCN and1. The energy of replacing the H₂O molecule in the inner sphere of complexes with a solvent molecule has been calculated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1762–1766, October, 1994.     

The substitution chemistry of RuCp* (temeda)Cl

Summary Halide abstraction from RuCp*(tmeda)Cl (1,tmeda=Me₂NCH₂CH₂NMe₂) with NaBPh₄ in CH₂Cl₂ leads to the formation of the sandwich complex RuCp*(⁶-C₆H₅BPh₃) (2). In the presence of CH₃CN (1 equiv.) and CO, however, the cationic complexes [RuCp*(tmeda)(CH₃CN)]⁺ (3) and [RuCp*(temeda)(CO)]⁺ (5) are obtained. In CH₃CN,tmeda is also replaced giving [RuCp*(CH₃CN)₃]⁺ (4). Complex1 reacts readily with terminal acetylenes HCCR, the products depending on the nature ofR (Ph, SiMe₃,n-Bu, COOEt). Thus, withR=Ph the ruthenacyclopentatriene complex RuCp*(,-C₄Ph₂H₂)Cl (6), withR=SiMe₃ the cyclobutadiene complex Ru(Cp*)(⁴-C₄H₂(1,2-SiMe₃)₂)Cl (7), and withR=n-Bu and COOEt the binuclear complexes (Cp*)RuCl₂(²:⁴-₂-C₄H₂(1,3-R)₂)Ru(Cp*) (8,9) are obtained. Furthermore, with diethyl maleate in the presence of 1 equiv. of LiCl,1 transforms into the new anionic complex Li[Ru(Cp*) (²-C₂H₂(COOEt)₂)Cl₂] (10). X-ray structures of2,3,4,7, and10 are included.

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Substitutionsreaktionen von RuCp*(tmeda)Cl

Zusammenfassung Chloridabspaltung von RuCp*(tmeda)Cl (1,tmeda=Me₂NCH₂CH₂NMe₂) mittels NaBPh₄ in CH₂Cl₂ führt zur Bildung des Halbsandwich-Komplexes RuCp*(⁶-C₆H₅BPh₃) (2), während in Gegenwart von CH₃CN oder CO die beiden kationischen Verbindungen [RuCp*(tmeda)(CH₃CN)]⁺ (3) und [RuCp*(tmeda)(CO)]⁺ (5) entstehen. In CH₃CN als Lösungsmittel wird sogartmeda unter Bildung von [RuCp*(CH₃CN)₃]⁺ (4) verdrängt. Komplex1 reagiert sehr leicht mit terminalen Alkinen HCCR, wobei die Produkte stark von der Natur des SubstituentenR (Ph, SiMe₃,n-Bu, COOEt) abhängen. Im Fall vonR=Ph entsteht der Ruthenacyclopentatrien-Komplex RuCp*(-C₄Ph₂H₂)Cl (6), mitR=SiMe₃ der Cyclobutadien-Komplex Ru(Cp*)(⁴-C₄H₂(1,2-SiMe₃)₂)Cl (7), und im Fall vonR=n-Bu und COOEt bilden sich die binuklearen Komplexe (Cp*)RuCl₂(²:⁴-₂-C₄H₂(1,3-R)₂)Ru(Cp*) (8,9). Überdies reagiert1 mit Maleinsäurediethylester in Gegenwart von LiCl zum neuen anionischen Komplex Li[Ru(Cp*) (²-C₂H₂(COOEt)₂)Cl₂] (10). Von2,3,4,7 und10 wurden die Kristallstrukturen bestimmt.

     

Synthesis and Crystal Structures of Copper(I) Complexes with N-Allylhexamethylenetetraminium Chloride Obtained in Different Acidic Media

The crystals of [(CH₂)₆N₄(C₃H₅)]Cu₂Cl₃ (I), [(CH₂)₆N₄(C₃H₅)]Cu₂Cl₃ (II), and [(CH₂)₆N₄(C₃H₅)]CuCl₂ (III) complexes were electrochemically synthesized (ac) from CuCl₂ · 2H₂O and N-allylhexamethylenetetraminium chloride in ethanol solutions at pH 6, 4.5, and 3. Their structures were determined using X-ray diffraction analysis (DARCh diffractometer, MoK radiation, /2 scan mode). Complex Icrystallizes in the monoclinic system: space group A2/a, a = 24.812(6) Å, b = 8.855(3) Å, c = 12.080(2) Å, = 89.21(3)°, and Z = 8. Complex II crystallizes in the triclinic system: space group P , a = 7.618(2) Å, b = 7.048(2) Å, c = 13.150(3) Å, = 97.50(2)°, = 92.70(2)°, = 100.74(2)°, and Z = 2. The crystals of complex III are orthorhombic: space group Pmn2₁, a = 7.478(2) Å, b = 8.827(2) Å, c = 9.662(3) Å, Z = 2. The organic cation in complex I acts as a tridentate ,,-ligand; that in complex II, as a bidentate ,-ligand. In complex III, the organic cation is involved in coordination with the copper(I) atom only through one nitrogen atom.     

Ionization potentials of halides. Substituent effects in Cl-, Br-, and I-centered radical cations

The first vertical ionization potentials (I) of halides HalX (Hal = Cl, Br, I; X is an inorganic or organic substituent) are linearly related to the inductive (_I), resonance (_R ⁺), and polarizability () constants of the substituents X (I = a + b_I + c_R ⁺ + d). As the atomic number of the Hal element in the Hal^·+X radical cations increases, the inductive interaction is strengthened while the polarizability interaction is weakened. Conjugation remains virtually independent of the Hal atom. The resonance _R ⁺-constants of the MX₃ (M = Si, Ge, Sn, Pb) substituents bound to the Hal^·+ radical cation centers were first calculated.     

The nature of the inductive effect of azinyl groups

The induction constants of azinyl groups are factored into two components, a -induction ( _X ) and a field (_F) component. It is shown that the _X constants of azinyl groups can be thought of as sums of contributions from the phenyl group and the endocyclic nitrogen atoms. A satisfactory correlation is found between the _F constants and the size and direction of the dipole moment of the heterocyclic substituents in the framework of the Kirkwood-Westheimer equation.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 672–676, May, 1987.     

Crystal and molecular structure of a crown-bridgedp-t-butyl-calix[4]arene (1:1) pyridine complex. Host-guest interaction model based on molecular mechanics analysis [1]

The crystal and molecular structure of a crownedp-t-butyl-calix[4]arene (1:1) pyridine complex is reported. Colourless transparent prismatic crystals (obtained from pyridine) C₅₄H₇₄O₈·C₅H₅N,a=13.486(4),b=15.193(4),c=16.432(5) Å, =116.44(4)°, space groupP2₁,Z=2,D _calc=1.02g cm^–3, CuK radiation =1.5418 Å (CuK )=4.99 cm^–1. Refinement was carried out using 1702 reflections withI>3(I) toR 0.12. The macrocycle shows a distorted cone conformation which defines an intramolecular apolar cavity whose elliptical aperture is 11.5×8.6 Å calculated as distances between the two opposite central C atoms of the Bu ^t groups. A molecule of pyridine is included in this cavity, whereas the intermolecular cavities of the host lattice remain empty. The influence of the guest molecule on the conformation of the calixarene-crown is discussed. Potential energy calculations are performed in order to understand the nature of the host-guest interactions responsible for the stabilisation of the complex. Evidence for stabilizing CH₃- interactions are obtained from the calculations. Supplementary Data relevant to this article have been deposited with the British Library as supplementary Publication No. SUP 82068 (9 pages).     

Determination of reactivity constants of 5-substituted 2-indolyl groups by means of13C NMR

Conclusions A series of 5-substituted 2-phenylindoles has been synthesized; the¹³C chemical shifts have been measured for these compounds in acetone, and these data have been used to determine the _I and _R ^O constants of the 5-substituted 2-indolyl groups. Relationships have been found for the estimation of the constants of any 5-substituted 2-indolyl group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 312–315, February, 1985.     

Synthesis of some 5′-O-amino acid derivatives of uridine as potential inhibitors ofUDP-glucuronosyltransferase

Summary In an attempt to develop potential inhibitors ofUDP-glucuronosyltransferase, some 5-O-amino acid derivatives of uridine were synthesized. N-protectedL-amino acids were coupled at the 5-O-position of 2,3-O-isopropylideneuridine by esterification employing the method of symmetrical anhydrides in presence of 4-dimethylaminopyridine, 5-O-(N-benzyloxycarbonyl-O-tert.butyl-L-threonl)-23-O-isopropylideneuridine (1), 5-O-(N-tert.butyloxycarbonyl-O-benzyl-L-seryl)-2,3-O-isopropylideneuridine and (2), 5-O-(N-tert.butyloxycarbonyl-L-valyl)-2,3-O-isopropylideneuridine (3), and 5-O-(N-tert.butyloxycarbonyl-L-valyl)-2,3-O-isopropylideneuridine (4) were obtained in good yield after column chromatography on silica gel. The treatment of2 withTFA/CH₂Cl₂ (6:1) at room temperature for 30 min led to a selective removal of theBoc group without deblocking of the 2,3-O-isopropylidene group of uridine. Treatment of2 withTFA/H₂O (5:1) at room temperature for 1 h, however, released bothBoc and 2,3-isopropylidene groups. TheZ group of1 was deprotected by catalytic hydrogenolysis over 10% Pd/C/ammonium formate.

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Synthese von 5-O-Aminosäurederivaten des Uridins als potentielle Inhibitoren derUDP-Glukuronosyl-Transferase

Zusammenfassung In einem Versuch, potentielle Inhibitoren derUDP-Glukuronosyl-Transferase zu entwickeln, wurden einige 5-O-Aminosäurederivate des Uridins synthetisiert. N-GeschützteL-Aminosäuren wurden durch Veresterung mit der 5-O-Position des 2,3-isopropylidenuridins gekuppelt (Methode der symmetrischen Anhydride in der Gegenwart von 5-Dimethylaminopyridin). Solcherweise wurden 5-O-(N-Benzyloxycarbonyl-O-tert.butyl-L-threonly)-2,3-O-isopropylidenuridin (1), 5-O-(N-tert.Butyloxycarbonyl-O-benzyl-L-seryl)-2,3-O-isopropylidenuridin (2), 5-O-(N-tert.Butyloxycarbonyl-L-leucyl)-2,3-O-isopropylidenuridin (3) und 5-O-(N-tert.Butyloxycarbonyl-L-valyl)-2,3-O-isopropylidenuridine (4) nach Säulenchromatographie (Kieselgel) in guter Ausbeute hergestellt. Die Behandlung von2 mitTFA/CH₂Cl₂ (6:1) bei Zimmertemperatur (30 min) führte zu einer selektiven Abspaltung derBoc-Gruppe ohne Deblockierung der 2,3-O-Isopropylidengruppe des Uridins. Eine Behandlung von2 mitTFA/H₂O (5:1) bei Zimmertemperatur für 1 Stunde führte hingegen zur Abspaltung sowohl derBoc als auch der 2,3-O-Isopropylidengruppe. DieZ-Gruppe von1 wurde durch katalytische Hydrogenolyse auf 10% Pd/C/Ammoniumformiat abgespalten.

     

Electronic structure of BF3-benzaldehyde

Two different models were assumed for BF₃-benzaldehyde: a charge transfer complex and a — one. The CNDO/2 and the Mulliken's population analysis were used. From the given numerical results we clearly conclude a — model. An electronic migration from benzaldehyde to BF₃ and other results of the population analysis are also discussed.     

Substituent effect and enthalpy-entropy compensation on the inclusion ofβ-cyclodextrin with 1-substituted naphthalenes

The inclusion complexation of-CD with 1-substituted naphthalenes has been investigated by fluorescence spectroscopy. It was observed that the association constants were influenced by the molar refraction (R _m), hydrophobic constant ( _x ), and Hammett constant ( _x ) of substituents in the guest compounds. The thermodynamic parameters G⁰, H ⁰, and S ⁰ determined by measuring the temperature-dependentK _a values shows that inclusion complex formation is enthalpy driven. The results are discussed in terms of enthalpy-entropy compensation.