Yu. Yu. Rusakov

Fluorescence quenching and laser photolysis of dipyrrolylbenzenes in the presence of chloromethanes

Fluorescence quenching of 1,4-bis(1H-pyrrol-1-yl)benzene, 1-(1H-pyrrol-2-yl)-1-(1-vinyl-1H-pyrrol-1-yl)benzene, and 1,4-bis(1-vinyl-1H-pyrrol-2-yl)benzene with chloromethanes (methylene chloride, chloroform, and carbon tetrachloride) in solvents with different polarities follows electron-transfer mechanism. The occurrence of an electron-transfer step is confirmed by formation of short-lived pyrrolylbenzene radical cations. An exception is quenching of fluorescence of 1,4-bis(1-vinyl-1H-pyrrol-2-yl)benzene in n-hexane in the presence of CCl4 and CHCl3 and in pure CCl4. In this case, neutral 1,4-bis(1-vinyl-1H-pyrrol-2-yl)benzene·-Cl radical is formed via recombination of 1,4-bis(1-vinyl-1H-pyrrol-2-yl)benzene radical cation and chloride anion. A relation was found between the nature of the short-lived species detected by laser photolysis and stable product obtained by stationary photolysis.

Reaction of 2-pyridylselenenyl bromide with divinyl selenide

Also published in Chemistry of Heterocyclic Compounds , 2012, 48 (7), pp 1129-1131 http://link.springer.com/article/10.1007/s10593-012-1115-y

13C-13C spin-spin coupling constants in structural studies: XL. Conformational analysis of N-vinylpyrroles

Conformational analysis of ten N-vinylpyrroles was performed on the basis of experimental 13C-1H and 13C-13C coupling constants and those calculated by high-level quantum-chemical methods, and principal relations between JCC and JCH values and stereochemical structure of these compounds were revealed.

Calculations of 29Si NMR shifts of organylsilanes by DFT taking into account solvent effects and relativistic corrections

The accuracy of calculations of the 29Si NMR chemical shifts of organylsilanes with different hybridization of C atoms in the substituents at the Si atom (sp3, sp2, and sp) was analyzed on the basis of the effective calculation scheme in terms of the density functional theory using the KT3 functional in combination with the ?-polarization consistent basis set pcS-3. Taking into account the influence of the medium in terms of the supermolecular solvate model and relativistic effects based on the full four-component Dirac scheme made it possible to achieve the extremely high accuracy of calculations of 29Si NMR chemical shifts of organylsilanes: 1 ppm for a span of 100 ppm. The contributions of solvent, relativistic, and vibrational corrections for the 29Si NMR chemical shifts are 3, 1, and 1 ppm, respectively, and taking them into account noticeably improves the agreement of calculation results with experiment. The relativistic shielding contribution to the absolute shielding constant of the Si atom is 12—13 ppm on the average, i.e., to ca. 3% in the relative expression.

Relativistic effect of iodine in 13C NMR chemical shifts of iodomethanes from quantum chemical calculations within the framework of the full four-component relativistic Dirac—Coulomb scheme

Abstract13C NMR shielding constants (chemical shifts) of iodomethanes were calculated within the framework of the full four-component relativistic Dirac—Coulomb scheme. As the number of iodine atoms in the molecule increases, the relativistic counterpart of the 13C NMR chemical shift increases from a few tens to several hundreds of ppm. Calculations of 13C NMR chemical shifts of organoiodine compounds should be performed at the relativistic level using relativistic Dyall’s basis sets dyall.vXz and dyall.xvXz (x = a, c, ac, ae; X = 2, 3, 4) of at least triple-zeta quality or at the correlated non-relativistic level taking into account relativistic corrections. Solvent effects are not of prime importance; however, taking into account the solvent corrections causes the mean absolute error of determination of the 13C NMR chemical shifts to decrease by 1—2 ppm.

Reaction of tellurium tetrachloride with hex-3-yne

Reactions of tellurium tetrachloride and its derivatives with alkynes are used for the preparation of compounds useful in the stereoselective synthesis of alkenes.1,2 The reaction of tellurium tetrachloride with both the terminal (phenylacetylene,2,3 tert butylacetylene4) and disubstitut ed arylacetylenes (diphenylacetylene,2,3 arylalkynes2) pro ceeds as a syn addition with the formation of Z products. It is believed that the mechanism of syn addition of tellu rium tetrachloride includes the formation of a four mem bered cyclic transition state.4 For a long time, the syn addition of tellurium tetra chloride was considered to operate for all the acetylene hydrocarbons.2—4 However, recently it was found that the reaction of tellurium tetrachloride with unsubstituted acetylene proceeded as an anti addition and led to the products with E configuration.5—7 There is no other liter ature examples of the anti addition of tellurium tetra chloride to acetylene hydrocarbons. In the present work, we describe an example of the anti addition of tellurium tetrachloride to the internal hex 3 yne with highly stereoselective formation of the product with E configuration (Scheme 1). The product is the ear lier unknown E (4 chlorohex 3 en 3 yl)tellurium trichlo ride (1), its yield was 95%. The process was carried out upon heating of the equimolar amounts of reagents in tetrachloromethane. Apparently, in this case the anti addition proceeds through the formation of the intermediate three mem bered tellurirenium intermediate. The formation of such three membered intermediates was suggested in the reac tions of sulfenyl and selenenyl chlorides with alkynes, pro ceeding as electrophilic anti addition.8 The reduction of compound 1 with sodium meta bisulfite in a two phase system CCl4—H2O led to earlier unknown bis(E 4 chlorohex 3 en 3 yl) ditelluride (2) in 82% yield (see Scheme 1).

Quantum-chemical calculations of NMR chemical shifts of organic molecules: XII. Calculation of the 13C NMR chemical shifts of fluoromethanes at the DFT level

Calculation was carried out of chemical shifts in 13C NMR spectra for a series of fluoromethanes CHnF4−n (n = 0–4) by the methods of the electron density functional theory GIAO-DFT taking in consideration the solvent effect in the framework of the polarizable continuum model Tomasi IEF-PCM. The best results were obtained at the use of Keal-Tozer KT3 functional combined with Pople standard basis sets 6-311G(d,p) and 6-311++G(d,p), and also with Jensen special set pcS-2 containing tight p-functions. The optimum reference in the calculation of chemical shifts in 13C NMR spectra for the fluoromethanes series is TMS.

An Effective Method for the Synthesis of 3,5-bis(halomethyl)-1,4-Oxaselenanes and their Derivatives

We report the first study of selenium dichloride and dibromide reactions with diallyl ether, aimed at the preparation of selenium-containing heterocyclic compounds. It was established that selenium dichloride reacted regio- and stereoselectively, giving cis-3,5-bis(chloromethyl)-1,4-oxaselenane in 70% yield. Selenium dibromide gave 3,5-bis(bromomethyl)-1,4-oxaselenane in 76% yield, as a mixture of cis and trans diastereomers. The obtained compounds were used for the synthesis of previously unknown 1,4-oxaselenanes: 3,5-bis(methoxymethyl)-, 4,4-dibromo-3,5-bis(chloromethyl)-, and 3,5-bis-(bromomethyl)-4,4-dichloro-1,4-oxaselenane. The diastereomers of 3,5-bis(halomethyl)-1,4-oxa-selenanes were found to undergo unusually facile isomerization.

Incomparably easy migration of functionalized enol substituent in pyrrole ring

Functionalized pyrroleьvьЄ enols, 2-(1-hydroxy-2.2-dicyanoethenyl)-1-methylpyrroles, at heating (75–135°C) unexpectedly readily rearranged in high yield into 3-isomers. Evidently the migration of the enol fragment involves a mesomeric zwitterion formed as a result of an intra- and intermolecular autoprotonation of the pyrrole ring by the acidic enol hydroxy group. Under similar conditions no migration of the ethenyl moiety occurred in 2-(1-hydroxy-2-carbamoyl-2-cyanoethenyl)-1-methylpyrroles. The quantum-chemical calculations (MP2/6-311G**) show a clear-cut distinction in the relative stability of 2- and 3-isomers of 1H- and 1-methylhydroxyethenylpyrroles: in the former case the 2-isomer is more stable, whereas in the 1-methyl-substituted compound, the 3-isomer.

Quantum-chemical calculations of NMR chemical shifts of organic molecules: XIV. Solvation effects in calculations of chemical shifts in 13C NMR spectra of chlorine-containing compounds

Analysis of precision factors in calculations of 13C NMR chemical shifts in the series of saturated and unsaturated organochlorine compounds was performed in the framework of the method of electron density functional theory GIAO-DFT-KT3/pcS-2 in the gas phase and with accounting for solvent effect by the polarized continuum model IEF-PCM. The accounting for solvation effects in calculations of 13C NMR chemical shifts within the framework of the IEF-PCM model is not fundamental for organochlorine compounds, yet it considerably improves the precision of calculations up to 2.5 ppm.