A spectroscopic method in studying the dissociation kinetics of hydrogen molecules

The actinometry method was used to study experimentally the kinetics of the formation of hydrogen atoms in a low-pressure glow discharge initiated in a hydrogen-argon mixture. Dependences of the steady-state concentration of hydrogen atoms on current and pressure have been obtained for the ranges i/R=1 to 16 mA/cm and pR=0.7 to 10 Torr·cm, respectively. It has been established that for discharge-activated hydrogen, when the temperature of the system varies only slightly, the recombination frequency parameter v_H=γ_HD_H/Λ² can be used. Ivanovo State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 13–17, May, 1999.     

Electrophilic 1,3-C→N− and-N→C− migrations in saturated systems

A new type of intramolecular electrophilic rearrangements involving the shift of COOAlk groups from carbon to an N-anionic center is considered. Carbanionic species with COOAlk groups at anionic centers containing no acidic hydrogen react unusually with alkyl(aryl) iso(thio)cyanates giving carbamates as a result of insertion of RNCX into the C−C bond. The kinetics and mechanism of insertion of aryl isocyanates into the C−C bond of the phosphonium zwitterion obtained from triisopropylphosphine and ethyl 2-cyanoacrylate are discussed. The reaction of α-carbanions derived fromN,N-disubstituted amides with methyl trifluoromethanesulfonate results inO-methylation. Some possibilities of back N→C⁻ migrations are considered. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1643–1648, September, 1999.     

Paramagnetic defects in gamma-irradiated Na/K-silicate glasses

Gamma-irradiated alkali silicate glasses of the variable composition 22xNa₂O · 22(1 ? x)K₂O · 3CaO · 75SiO₂ have been studied using the electron paramagnetic resonance (EPR) method. It has been established that, upon the successive replacement Na ?? K in the two-alkali silicate glass, the EPR spectrum of hole centers on nonbridging oxygen atoms can be represented as a superposition of signals from the oxygen centers HC ₁(Na), HC ₂(Na), HC ₁(K), and HC ₂(K), which are characteristic of single-alkali silicate systems. The concentration dependences of hole and electron paramagnetic centers do not exhibit specific features that can be interpreted as a manifestation of the ??mixed-alkali effect.?? The results obtained have been discussed taking into account the extended model of centers on nonbridging oxygen atoms.     

Gadolinium ion localization in RbPb2Cl5 crystals

The spectrum of the electron paramagnetic resonance of high-spin triclinic Gd³⁺ centers in lead-rubidium chloride single crystals has been studied. The spin Hamiltonian parameters have been determined. It has been concluded that the rare-earth ion is localized at the lead site whose environment is a tricapped trigonal prism.     

meso-spacer influence on properties of zinc(II) complexes with 2,3′- and 3,3′-bis(dipyrrolylmethenes)

The study and comparative analysis of spectral-luminescent characteristics (absorption and fluorescence spectra), of quantum yield, and fluorescence life time in solutions, of lability in proton-donor media, solid phase thermal stability in air oxygen and argon was carried out for binuclear zinc(II) helicates with decamethyl-substituted 2,3′- and 3,3′-bis(dipyrrolylmethenes). The influence of molecular structure features of the ligands on the physicochemical properties of helicates was discussed.     

Reaction of α-cyanoacrylates with functionally substituted thiols,ethanedithiol, and hydrogen sulfide

Functionally substituted thiols, i.e., thioglycolic acid and cysteamine and cysteine hydrochlorides, facilely undergo addition at the double bond of -cyanoacrylates, forming the corresponding adducts in quantitative yields: RSCH₂CH(CN)COOR [R=CH₂COOH; CH₂CH₂NH₂·HCl; CH₂CH(COOH)NH₂·HCl]. Under similar conditions, the reaction with ethanedithiol gives the diadduct [CH₂SCH₂CH(CN)COOR]₂; the monoadduct HSCH₂CH₂SCH₂CH(CN)COOR is formed in a significantly lower yield. Hydrogen sulfide does not undergo addition to -cyanoacrylate in the absence of a catalyst; S[CH₂CH(CN)COOR]₂ is formed quantitatively in the presence of Et₃N. In the presence of triethylamine, this sulfide undergoes intramolecular cyclization (the Ziegler-Thorpe reaction) with formation of 4-amino-5-cyano-3,5-bis(ethoxycarbonyl)thiacyclohex-3-ene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2816–2820, December, 1991.     

Preparation of brassylic acid from 5,6,7,8,9,10,11,12,13,14-decahydrocyclododeca[1,2-d]pyrimidine(1H, 3H)-2,4-dione obtained by the condensation of cyclododecanone and urea or biuret

A simple method is proposed for the preparation of brassylic acid by the alkaline hydrolysis of 5,6,7,8,9,10,11,12,13,14-decahydrocyclododeca[1,2-d]pyrimidine(1H, 3H)dione-2,4, which is the product of the condensation of cyclododecanone with urea or biuret. The condensation of the cyclododecanone with thiourea proceeds differently, leading to 5,6,7,8,9,10,11,12,13,14-decahydrocyclododeca[1,2-d]pyrimidine(1H, 3H)spirocyclododecane-2-thione-4.A. N. Nesmeyanov Institute of Organometallic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 226–229, January, 1992.     

Complexation between decamethyl-3,3′-bis(dipyrrolylmethene) and zinc(II), copper(II), and cobalt(II) acetates

Decamethyl-3,3′-bis(dipyrrolylmethene) dihydrobromide H₂L · 2HBr (H₂L is bis(3,4,7,8,9-pentamethylpyrrol-3-yl)methane), which is the simplest representative of a novel class of oligo(dipyrrolylmethenes) belonging to chromophore chelating nonmacrocyclic ligands, were examined by ¹H NMR, IR, and electronic absorption spectroscopy. Complexation reactions of H₂L · 2HBr with M(AcO)₂ (M = Zn(II), Cu(II), and Co(II)) in DMF at 298.15 K were monitored by electronic absorption spectroscopy and studied by the molar ratio method. The thermodynamic constants K ⁰ of these reactions were estimated. The d metal ions coordinate H₂L to give the binuclear homoleptic complexes [M₂L₂]. The reactions proceed through the intermediate binuclear heteroleptic complex [M₂L(AcO)₂] detected by spectroscopic methods. The thermodynamic stabilities of [M₂L₂] and [M₂L(AcO)₂] increase when moving from Cu(II) to Zn(II) and Co(II). The probability of formation and stability of [M₂L₂] containing 3,3′-bis(dipyrrolylmethene) are substantially higher than those of analogous complexes with the 2,2′-isomer (decamethyl-2,2′-biladienea, c). The low K ⁰ values for the complexation between H₂L and Cu(AcO)₂ are due to slow oxidation of the biladiene ligand into a bilatriene with participation of Cu²⁺ ions.     

Reversible isomerization of chromogenic dimers and the nature of azulene chromaticity

The spectra of azulene solutions in siloxane and heptadecane were studied. The VIS band (435–714 nm) associated with the color blue was shown to transform reversibly as a result of a temperature increase and to assume a likeness to the less intensive VIS band typical for solutions in polar ethanol and dibutyl phthalate. It was concluded that supramolecular dimers rather than individual molecules are the chromogens of azulene, just as in the case of phthalocyanine, triphenylmethane, xanthene, and thiazine dyes. Clar’s conclusions regarding the nature of the visible band of azulene absorption and the mechanism of reversible thermal discoloration of azulene solutions in high-boiling-point hydrocarbons are consequently wrong. It was established that the thermochromism of azulene solutions is actually not associated with the isomerization of azulene molecules into nonplanar nonaromatic molecules but with the reversible isomerization of dimeric structures, accompanied by a change in the positions of the aromatic molecules relative to one another. The corresponding equilibrium is somewhat endothermic: ΔH = 6.6 kJ/mol, ΔG ^o ≈ − 1.45 kJ/mol. Based on these results, it was concluded that light absorption changes the energetic state of the dimeric structures (transition S _D→ S _D^*) without leading to electron transfer in single molecules according to the scheme S ₀ →S ₁. That is, the traditional idea that Kasha’s law is violated when azulene fluoresces is incorrect, since the radiation comes from the S ₁ level and not from the S ₂ level, as is stated in the literature.     

Synthesis of (m-carboran-9-yl)ferrocene and (m-carboran-9-yl)cymantrene

Cross-coupling reactions of 9-iodo-m-carborane with ferrocenylzinc chloride or cymantrenylzinc chloride catalyzed by (Ph₃P)₂PdCl₂ result in the formation of (m-carbo ran-9-yl)ferrocene and (m-carboran-9-yl)cymantrene, respectively. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 542–543, March, 1998.