Reactions of chromium atoms with chloromethanes

The rate constants of the gas-phase reactions of the chromium atom with CC1⁴, CHC1₃, and CH₂Cl₂ were measured behind shock waves at 800–1400 K. The results are presented in the Arrhenius form (the activation energy is given in kJ/mol):k _{CCl 4} = 10^14.32±0.36exp[-(2.0±7.5)/RT],k _{CHCl 3} = 10^14.72±0.21exp[-(18.5.±4.0)/RT, andk _{CH 2 Cl 2}> = 10^14.33±0.16exp[-(24.1±3.1)/RT]cm³mol^-1s^-1.     

Diazabicycloalkanes with bridgehead nitrogen atoms

By heating 1-(2-hydroxyethyl)benzo[b]-1-azonium-4-azabicyclo-[2.2.2]octene halides in anhydrous solvents or via thermolysis, opening of the bicycle occurs with formation of the corresponding N-(2-hydroxyethyl)-N-(2-haloethyl)-1, 2,3,4-tetrahydroquinoxalines. In the presence of base, fission of the hydroxyethyl group principally occurs.For Communication 25, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1091–1094, August, 1992.     

Pyrimido[5,4-b]quinolines. II. Reactions at the heterocyclic ring-carbon and nitrogen atoms

10-Chloro-7,8-dimethylpyrimido[5,4-b]quinolin-2,4(1H,3H)dione (I) was unreactive toward ammonia but it reacted with 2 molecules of n-butylamine, presumably via Dimroth-type ring-opening and closure, to give the N₃-butyl, N₁₀-butylamino derivative (IV). In similar reactions of 10-chloro-2,4-dimethoxy-7,8-dimethylpyrimido[5,4-b]quinoline (II) only the 4-meth-oxyl was displaced by either ammonia or n-butylamine. Alkyllithium reagents also displaced the 4-methoxyl as well as added to the 3,4 double bond of II to yield the corresponding gem-dialkyl substituted (C₄) derivatives; the C₁₀ chlorine remained unreactive. 2,4-Dimethoxy-7,8-di-methylpyrimido[5,4-b]quinoline-10-one (III) could be alkylated only in the form of the thallium salt. Treatment of the benzyl derivative of III with methylmagnesium bromide led only to the displacement of the 4-methoxyl by a methyl group.     

Reactions of nitrile oxides with nitrogen oxides. 2. Reactions with nitrogen monoxide and nitrogen sesquioxide

We have studied the reactions of aromatic nitrile oxides with nitrogen monoxide and nitrogen sesquioxide. It was shown that nitrogen monoxide removes an oxygen atom from the nitrile oxide with formation of the corresponding nitrile and nitrogen dioxide. The reaction products with nitrogen sesquioxide are formed as a result of reactions of the nitrile oxide with nitrogen monoxide and nitrogen tetroxide.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1623–1625, July, 1990.     

Reactions of nitrile oxides with nitrogen oxides. 1. Reactions with nitrogen tetroxide

We have studied the reaction of nitrile oxides with nitrogen tetroxide. It was shown that the reaction is selective: acetonitrile oxide yields ethylnitrolic acid, -oximinophenylacetonitrile oxide gives a mixture of isomers of phenylnitrofuroxan, and aromatic nitrile oxides give aryltrinitromethanes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1620–1622, July, 1990.     

Scattering of nitrogen molecules by silver atoms

We present a quantal study of the rotationally elastic and inelastic scattering of Ag and N(2), with the nitrogen molecule treated as a rigid rotor. The two-dimensional potential energy surface of the AgN(2) complex is obtained ab initio by means of the spin unrestricted coupled-cluster method with single, double, and perturbative triple excitations. The global minimum is found to be located at an internuclear distance of 8.13 a(0) and an angle of 127.2°. The long-range part of the potential is constructed from the dynamic electric dipole polarizabilities of Ag and N(2). Elastic, excitation, and relaxation cross sections and rates are calculated for energies between 0.1 and 5000 cm(-1). The momentum transfer cross sections and rates are also computed. Finally, we compare the cross sections for Ag-N(2) and Na-N(2) to explore the possibility of using silver instead of sodium in experimental tests.     

Reactions of complexed small nitrogen heterocycles

Complexes of ethyleneimine and trimethyleneimine have been examined. Their thermal reactions are strictly controlled, giving polyamine complexes, which can also be obtained directly from the polyamines.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1108–1114, May, 1990.     

Reactions of hydrogen atoms with met-enkephalin and related peptides

The reactions of hydrogen atoms with enkephalins and related peptides have been investigated by radiolytic methods in aqueous solutions and lipid vesicle suspensions. Pulse radiolysis experiments indicate that methionine residue (Met) is the main target. In Met-enkephalin (Tyr-Gly-Gly-Phe-Met) the attack of the hydrogen atom occurs to about 50 % on Met with formation of methanethiyl radical. The remaining percentage is divided roughly evenly between Tyr and Phe. With Leu-enkephalin (Tyr-Gly-Gly-Phe-Leu) the site of attack is limited to Tyr and Phe. Using a peptide-liposome (that is, 1-palmitoyl-2-oleoyl phosphatidylcholine vesicles) model, the cis-trans isomerization of phospholipids could be detected due to the catalytic action of thiyl radicals. The radiation chemical yields of the H(.) and, consequently of CH(3)S(.) radical, was modulated by the experimental conditions and the nature of peptide. Large amounts of trans lipids observed in phosphate buffer vesicle suspensions indicated the efficient role of double-bond isomerization as marker of Met-containing peptide damage.     

Reactions of high translational energy hydrogen atoms with propane

The reactions of translationally excited deuterium atoms with propane have been investigated by use of photochemically produced atoms of 157kJmol(-1) initial energy. The reaction mechanism was tested by comparing the results for the DBr scavenged system to those where Br(2) was used as radical scavenger. Values were obtained for the fraction of atoms undergoing "hot" reaction on collision with propane, and the relative cross sections for the interaction of deuterium atoms with propane and DBr. The effect of the initial energy of the "hot" atoms is discussed.     

Reactions of tetrachloropyridazine with aliphatic nitrogen nucleophiles

Nucleophilic aromatic substitution reactions of tetrachloropyridazine with a series of aliphatic primary and secondary amines led selectively to products arising from replacement of chlorine at the 4‐position in all cases. The structures of the products were unambiguously confirmed by X‐ray crystallography. Substitution occurs at the most activated site para to ring nitrogen, despite the possible steric hindrance to substitution by adjacent chlorine atoms, reflecting the activating influence of ring nitrogen meta to the site of attack. N,N′‐Dimethylethylene diamine gave a mixture of [6,6] ring fused products following initial substitution at the 4‐position.     

Reactions of neutral gas-phase yttrium atoms with two cyclohexadiene isomers

The reactions of neutral ground-state yttrium (Y) atoms with 1,3- and 1,4-cyclohexadiene (CHD) were studied using crossed molecular beams. Formation of YC(6)H(6) + H(2) and YH(2) + C(6)H(6) was observed for both isomers at collision energies (E(coll)) of 31.3 and 13.0 kcal/mol. Measured product branching ratios at E(coll) = 31.3 kcal/mol indicated that YH(2) + C(6)H(6) was the dominant channel, accounting for >97% of the products. An additional minor product channel, YC(4)H(4) + C(2)H(4), was observed for 1,3-CHD at the higher E(coll). The reaction threshold for YC(4)H(4) formation was determined to be 29.5 ± 2.0 kcal/mol based on fits to the data.     

Two-photon laser-induced fluorescence in oxygen and nitrogen atoms

Two-photon absorption is used to populate the 3p ³P state of O and the 2s²2p²3p⁴D^o state of N in a flow discharge. Exciting photons are produced by anti-Stokes Raman frequency conversion of tunable UV laser radiation; the resulting near IR fluorescence from the excited state yielded lifetimes, quenching rates, and relative two-photon transition probabilities.     

Diazabicycloalkanes with nitrogen atoms in bridgehead positions.

1-Methyl-1-(-haloethyl)-1,2,3,4-tetrahydroquinoxalinium salts were synthesized and the dependence of the hydrolysis and cyclization rate constants on the acidity of the medium and presence of halide was found. It was determined that the monocations of tetrahydroquinoxalines participate in the formation of the benzo[b]-1,4-diazabicyclo[2.2.2]octene system, since blocking the free electron pair of the tertiary nitrogen atom with a methyl substituent significantly accelerates the cyclization and suppresses the hydrolytic side reaction.For Communication 17, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 372–378, March, 1989.     

Synthesis of pyrimidinophanes containing nitrogen atoms in polymethylene bridges

The reactions of 1,3-bis(-bromobutyl- or -pentyl)-6-methyluracil with 1,3-bis(-ethylaminobutyl- or -pentyl)-6-methyluracil afforded pyrimidinophanes containing N atoms in bridging polymethylene chains. Individual geometric isomers of pyrimidinophanes were isolated. The structure of one of these isomers was established by X-ray diffraction analysis. Quaternization of the bridging N atoms with o-nitrobenzyl bromide gave rise to water-soluble pyrimidinophanes.     

Reactions of photogenerated fluorine atoms with molecules trapped in solid argon

Isolated radicals^.NH₂ and radical-molecule complexes^.NH₂−HF, which are products of the reactions of mobile fluorine atoms with NH₃ molecules in solid argon, were identified by EPR spectroscopy. The isotropic HFC constants of the complex (a _N=1.20,a _H=2.40, anda _F=0.70 mT) were determined experimentally. The constant of isotropic HFC with the nucleus of hydrogen atom of the HF molecule is less than 0.1 mT. This assignment was confirmed in the experiments on isotope substitution of atoms (H→D),¹⁴N→¹⁵N) in the NH₃ molecule. According to quantum-chemical calculations, the free complex^.NH₂−HF has a planar structure withC ₂, summetry and a binding energy of 12 kcal mol⁻¹. Optimization of the arrangement of the complex in the crystal showed that its structure is only slightly distorted in the Ar lattice so that the equilibrium configuration is close to that obtained from gas-phase calculations. Different ratios of relative intensities of the proton triplet lines in the EPR spectra of isolated^.NH₂ radicals and^.NH₂−HF complexes were qualitatively explained by different heights of the barriers to rotation of the NH₂ fragment in the Ar lattice.     

Reactions of photogenerated fluorine atoms with dopant molecules in solid argon

The products of UV photolysis of ternary Ar?CH₄(CD₄)?F₂ mixtures (1:c:c ₀,c, c ₀=0.001–0.01) at 13–16 K were identified by ESR and FTIR spectroscopy. These products are^?CH₃ (^?CD₃) radicals of typesI andII and molecular CH₃F?HF complexes. The latter were characterized by the IR bands of the stretching C?F (1003 cm^?1) and H?F (3774 cm^?1) vibrations. The ESR spectra of radicalsI are asymmetric. The anisotropy of theg-factor (Δg～10^?3) of radicalI indicates that the structure of the radicals is nonplanar. The ESR spectrum of the typeII radical is identical to that of matrix-isolated^?CH₃ (^?CD₃) radicals with the planar structure (Δg<5·10^?5). Under the experimental conditions, the amount of complexes formed in the photolysis is equal to 0.022·c. When the photolysis is ceased, radicalI disappears after ≈10³ s and radicalII is stabilized. The limiting concentrations of the stabilized^?CH₃ and^?CD₃ radicals are equal to 2·10^?2·c and 2·10^?3·c, respectively. A mechanism of the formation of the products is suggested. It is based on the assumption that both matrix-isolated CH₄ and F₂ and their heterodimers CH₄?F₂ are present in the samples and it takes into account the long-range migration of translationally excited flourine atoms. The CH₃F?HF complexes and radicalsI are generated by the photolysis of the CH₄?F₂ heterodimers. The decay of radicalsI is caused by geminate recombination of proximate F...CH₃ pairs. RadicalsII are formed in the reaction of translationally excited fluorine atoms with isolated CH₄ (CD₄) molecules.