S N H reactions of pyrazine N-oxides and 1,2,4-triazine 4-oxides with CH-active compounds

Nucleophilic substitution of hydrogen in pyrazine N-oxides under the action of CH-active compounds requires activation with acylating agents. This activation facilitates aromatization of intermediate ^H adducts via elimination of the acid residue to form substituted pyrazines. More electrophilic 1,2,4-triazine 4-oxides react with carbanions derived from CH-active compounds without additional activation according to a scheme, which has previously been unknown for azine N-oxides. This scheme involves aromatization of ^H adducts through elimination of water by the E1cb mechanism. The reaction products occur in DMSO-d₆ solutions predominantly as 6-methylene-1,6-dihydropyrazines and 5-methylene-4,5-dihydro-1,2,4-triazines.     

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).     

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.     

Regioselectivity of Nucleophilic Attack on the Reactions of 1,2,4-Triazine 4-Oxides with Certain C-Nucleophiles

The addition of CH-active compounds to 6-aryl-1,2,4-triazine 4-oxide is reversible and occurs under conditions of kinetic control at position 5 of the heterocycle to form cyclic C(5)-^H adducts. Under conditions of thermodynamic control the nucleophilic attack is directed to position 3 of the heterocycle and is accompanied by its opening to form the more stable open chain addition products. Attack of ethylmagnesium bromide is directed exclusively to the 5 position of the 6-aryl-1,2,4-triazine 4-oxides as a result of the irreversibility of the given reaction.     

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.     

Reactions with β-cyanoethylhydrazine,III. A new approach for the synthesis of substituted 3,5-diaminopyrazole and 1,2,4-triazoles

The reactivity of -cyanoethylhydrazine toward enaminonitrile and aroyl isothiocyanates is reported. A variety of 3,5-diaminopyrazole and ³-1,2,4-triazolin-5-thione derivatives could be prepared.

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Reaktionen mit -Canyethylhydrazin, 3. Mitt.: Ein neuer Weg zur Synthese von substituierten 3,5-Diaminopyrazolen und 1,2,4-Triazolen

Zusammenfassung Es wird über die Reaktivität von -Cyanethylhydrazin gegenüber Enaminonitril und Aroylisothiocyanaten berichtet. Es konnte eine Reihe von 3,5-Diaminopyrazol-und ³-1,2,4-Triazolin-Derivaten hergestellt werden.

     

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).     

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.     

Theoretical assignments of the electronic spectrum of acetylene

Non empirical calculations of energies and properties of some excited states of acetylene are presented. A frozen core approximation is used and excitations to , and MO's are taken into account. Both valence and Rydberg states are considered. Assignments of the UV and electron impact spectra are proposed and some questions are raised.     

1H NMR Detection of σ-Adducts in S NH Reactions of Nitroquinolines with Chloromethyl Phenyl Sulfone

The intermediate -adducts of chloromethyl phenyl sulfone with 3-nitro-, 5-nitro-, 6-nitro-, 7-nitro- and 8-nitroquinoline are detected by ¹H NMR spectroscopy.     

Regression Analysis for the Host–Guest Interaction of β-Cyclodextrin with Mono- and 1,4-Disubstituted Benzenes

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.     

Interpretation of AC Conductivity of Lightly Doped Conducting Polymers in Terms of Hopping Conduction

The ac conduction of most disordered materials shows a regime of constant dc conductivity (0) at low frequencies and a crossover to a frequency-dependent regime of the type A ^s at high frequencies. We discuss the physical origin of this behavior and the interpretation of the onset frequency of excess ac conduction, _c , in terms of models for hopping conduction of polaronic carriers in a disordered medium. We emphasize the central role of the critical hopping rate in the percolation lattice for determining both (0) and _c . We show the behavior of () for lightly doped polypyrrole samples at different stages of doping, and we discuss the significance of frequency dispersion effects for electrochemical measurements.     

Correlation of IR parameters with reactivity characteristics for the hydrazides of carboxylic acids

Measurements have been made of the frequencies of the N-H and C=O stretching modes in dilute solution in CCl₄ for 23 aliphatic and aromatic substituted hydrazides of carboxylic acids. These are compared with the (⁰) Taft constants. Measurements have also been made of the basicity constants at 25 in water and the rate constants for reaction with phenyl isocyanate at 25. Correlation equations are derived for the transfer of electronic effects across the -CONH-bridge. It is found that the sign of the reaction constant in the correlation of with ⁰ reverses on passing from aromatic amines to amides via the hydrazides of carboxylic acids.We are indebted to L. M. Litvinenko and A. F. Popov for a discussion of the results.     

Electronic effect of the 1-[η5-cyclgpentadienyl-η5-(3)-1,2-dicarbollyliron(II)] group

Conclusions The Taft method was used to determine the electronic effect of the 1-[⁵-cyclopenta-dienyl-⁵-(3)-1,2-dicarbollyliron(II) ] group which displays strong electron-donor properties: _I=–0.22 and _R=–0.20.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1449–1451, June, 1985.     

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.     

Synthesis of 2β, 3β, 14α-trihydroxy-Δ4,7-6-ketosteroids and their derivatives

A scheme using -sitosterol as an example for synthesizing 2, 3, 14-trihydroxy-^4,7-6-ketosteroids and their derivatives from 3-hydroxy-⁵-steroids was developed.Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, 220141, Belarus, Minsk, ul, akad. Kuprevicha, 5/2. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 244–248, May–June, 2000.     

New notions of active surface composition of reforming catalysts

Some peculiarities of adsorption and catalytic properties of electron deficient platinum atoms (Pt) in reforming catalysts are presented. It appears possible to improve catalysts modifying Pt centers with -donor molecules.     

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.     

Electron structure of the V2 molecule derived from DV-Xα data

Conclusions The electron structure of the V₂ molecule has been calculated by means of the DV-X method. The configuration 3_u ⁴6_g ²7_g ²(l_g)² has been obtained for the ground state, which corresponds to a quintuple bond, and the equilibrium state 1.78 Å. The term of the ground state³_g ^– and the bond length are in agreement with the experimental data.Translated from Izvestiya Akadeinii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 232–235, September, 1985.The authors wish to express their gratitude to A. N. Ivanov and V. K. Gryaznov for the provision of the program for the calculation of the atomic Hartree-Fock functions.     

Ring-Ring Tautomerism in the Series of Isoxazolidine and Δ2-Isoxazoline Derivatives

We have studied the reaction of 5-hydroxy-3,3,5-trimethylisoxazolidine and 5-hydroxy-3,5-dimethyl-²-isoxazoline with derivatives of thiosemicarbazide and also thiocarbonohydrazine. Both reactions serve as a method for synthesis of the previously unknown 5-thiosemicarbazido(thiocarbonohydrazino)isoxazolidines and -²-isoxazolines. ¹H and ¹³C NMR spectroscopy revealed a tendency of the indicated compounds toward ring-chain and ring-ring tautomeric conversions in solutions involving the 1,2,4-triazolidine, ²-pyrazoline, and 1,2,4,5-tetrazine rings.