A study of the electronic structure and properties of the propargyl radical

By means of B3LYP/6-311++G(3df,3pd) the electron density distribution in the propargyl radical CH₂CCH is obtained. Within the Quantum Theory of Atoms in Molecules the phenomenon of conjugation and the spin density distribution of the unpaired electron in CH₂CCH are studied at the qualitative level. Characteristics of the electronic structure of CH₂CCH and its parent molecules CH₃–C≡CH and CH₂=C=CH₂ are compared. With the use of the rigid rotator-anharmonic oscillator model the thermodynamic properties of the propargyl radical and enthalpies of bond cleavage in propyne and allene are calculated in the temperature range 298-1500 K. The relationship between the electronic and thermodynamic properties of CH₂CCH is considered and its conjugation energy is calculated.     

The inductive effect of a radical center and transferability of the properties of functional groups in <Emphasis Type="Italic">n</Emphasis>-alkyl radicals

Electron density distribution in n-alkyl radicals (from ethyl to n-octyl) was studied by the B3LYP/6-311++G(3df,3pd) DFT method. The theory of atoms in molecules was used to show that the inductive effect of a free valence extends to two neighboring CH₂ groups. The electronegativities χ(C^?H₂) > χ(CH₃) > χ(CH₂) of groups and χ(C^?) > χ(H) > χ(C) atoms were qualitatively determined. The group method for calculating the enthalpies of formation of n-alkyl radicals Δ_f H°(n-C _n H_{2n+ 1}, n > 5) was substantiated.     

Electron affinity and substituent effects in radical anions

The first vertical electron affinities EA of 13 series of molecules and free radicals D(X _i ) _n are related to the inductive (σ _I ), resonance (σ _R ^? ), and polarization (σ_α) parameters of substituents X _i by the dependences EA = EA _H + aΣσ _I + bΣσ _R/? + cΣσ_α: In radical anions D^+·(X _i ) _n , compared to radical cations D^+·(X _i ) _n , the polarization interaction is weaker or similar in magnitude but has an opposite sign. The previously unknown resonance parameters σ _R ^? of substituents SiMe₃ and CH₂SiMe₃ bound to the radical anion center H₂C=CH^?· were calculated.     

The equilibrium structures of the Li[C<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>]<Subscript>1</Subscript> (<Emphasis Type="Italic">n</Emphasis> = 7–12) complexes and their alternation depending on <Emphasis Type="Italic">n</Emphasis>

The equilibrium geometric configurations of the Li[C _n ]₁ (n = 7–12) complexes, where [C _n ]₁ is a cylindrical hydrocarbon containing the simplest zigzag nanotube fragment, were determined by the density functional theory method with the PBE0 exchange-correlation functional. Analytic molecular orbital (MO) estimates were obtained for isolated [C _n ]₁ hydrocarbons in the Hückel approximation. The appearance of nonbonding MOs for hydrocarbons with even n was demonstrated. Equilibrium structure types were found to alternate as n increased. This alternation correlated with the behavior of the frontier orbitals of the [C _n ]₁ hydrocarbon. At odd n, the Li atom was situated near the boundary of the π electron density of the bracelet, and the complex had C _s symmetry. Complexes with even n had the C _2v point group, and lithium was situated in the inner cylinder cavity above the center of one of benzene rings.     

Theoretical study of stepwise chlorinated aluminide clusters Al<Subscript>13</Subscript>Cl<Stack><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript><Superscript>−</Superscript></Stack> (<Emphasis Type="Italic">n</Emphasis> = 1–9)

The electronic and geometric structures, energy stabilities, normal mode frequencies, and spin density distributions (in radicals) of different stepwise-chlorinated aluminum clusters Al₁₃Cl _n ^? (n = 1–9) are calculated within the B3LYP approximation of the density functional theory using 6-31G* and 6-311+G* basis sets. The results are compared with analogous computation data on hydrides Al₁₃H _n ^? (n = 1–12) obtained at the same level. The general qualitative pattern for related series of hydrides, chlorides, and iodides (as well as fluorides and bromides) turns out to be similar in many respects. For all Al₁₃X _n ^? clusters with different electronegative substituents X, there is a set of a considerable number of low-lying closely spaced inner isomers (with a centered icosahedral cage), marquee isomers, and outer isomers (capped). The effects found by calculations in centered icosahedral isomers—localization of spin density on the trans-Al* atom in radical anions and its associated trans addition rule for an even substituent and the zigzag (odd-even) dependence of the energies D _n (X) of successive addition of substituents X to the metal cage on n described in the framework of the molecular model of the valence states of the Al ₁₃ ^? superatom—should also be shared by many Al₁₃X _n ^? series with different X’s. The differences between hydrides Al₁₃H _n ^? and chlorides Al₁₃Cl _n ^? of the same type are quantitative. For the hydrides, inner isomers are preferable in the first half of the series (n = 1–6); and in the second half (n = 7–12), outer isomers are more favorable. For the chlorides, icosahedral isomers are preferable only at the very beginning of the series. In the other cases, nonicosahedral structures are most favorable, for which the situation becomes very complicated due to the large number of position isomers and the aforementioned simple rules found for centered icosahedral structures are fulfilled to a considerably less extent or not at all.     

Copolymers of Maleic Anhydride and Methylene Alkanes: Synthesis,Modification, and Pour Point Depressant Properties

Copolymers with the equimolar composition and presumably alternating microstructure are synthesized by the radical copolymerization of methylene alkanes, the products of dimerization of α-olefins with the general formula RCH₂CH₂C(=CH₂)R (R = n-C₄H₇, n-C₆H₁₃, n-C₈H₁₇, n-C₁₀H₂₁, n-C₁₂H₂₅), with maleic anhydride. The products of reactions between the obtained copolymers and 1-octadecanamine or 1-octadecanol are isolated and spectrally characterized. The depressor efficiency of the copolymers with respect to the solutions of paraffins in n-alkanes is studied. Qualitative differences between the copolymers of maleic anhydride with methylene alkanes and reference copolymers based on 1-octadecene are estimated using vibrational viscometry combined with analysis of the size and morphology of paraffin crystals. It is shown that the copolymers with methylene alkanes more effectively decrease the cold filter plugging point (CFPP) of paraffin solutions in n-decane.     

Synthesis and crystal structure of the equimolar complex of copper(I) cyanide with 3,3′-[ethane-1,2-diylbis(oxy)]dipropanenitrile

Complex [Cu(CN)(NC(CH₂)₂O(CH₂)₂O(CH₂)₂CN))] is obtained by the heating of copper(I) cyanide with 3,3′-[ethane-1,2-diylbis(oxy)]dipropanenitrile (DPN) followed by slow cooling. The X-ray diffraction analysis shows that the crystals are monoclinic, space group C2/c, a = 12.183(2), b = 10.667(2), c = 8.4700(13) Å, β = 92.444(10)°, V = 1099.7(3) ų, Z = 4. The structure is built of infinite zigzag fragments [Cu(CN)(DPN)] _n . The tetrahedral environment of the copper atom includes two cyano groups of the ligand and two cyano groups of the inorganic fragment.     

Determination of the molecular masses of tetrafluoroethylene telomers by gel-permeation chromatography

Gel-permeation chromatography has been employed to study the molecular-mass distribution of tetrafluoroethylene telomers prepared through γ irradiation of 0.05–0.56 mol/l monomer solutions in acetone. The molecular-mass-retention-volume V _R calibration dependence has been plotted from chromatograms of perfluoroenanthic and perfluoropelargonic acids (F(CF₂-CF₂) _n COOH; n = 3 or 4, respectively). The measured V _R-log n curve is located parallel to that plotted earlier for oligo(oxyethylene glycol)s (OH-(CH₂-CH₂O) _n -OH) and is shifted along the volume axis. The shift value is determined by the ratio between logarithmic volumes of chain units of these oligomers. The shift agrees with the assumption that the retention volumes of oligomers with the same spatial chain structure are proportional to the logarithm of the ratio between their van der Waals volumes. This assumption is supported by the quantum-chemical calculation of the molecular volumes of oligomers composed of (CH₂-CH₂) _n , (CH₂-CH₂O) _n , and (CF₂-CF₂) _n fragments. As the concentration of tetrafluoroethylene in the initial solution is increased, the average length of (CF₂-CF₂) _n chains increases from \(\bar n\) ≈ 3 to \(\bar n\) ≥ 8. The maximum values of n = 12–15 are determined by the solubility limit of telomers in THF.     

Kinetics of Isothermal Pyrolysis of Iodomethanes in the Gas Phase

The limiting step of the isothermal pyrolysis of gaseous iodomethane (CH₃I → 3/4CH₄ + 1/2I₂ + 1/(4n)C _n ) and diiodomethane (CH₂I₂ → 1/2CH₄ + I₂ + 1/(2n)C _n ) are the reactions 2CHI → C₂ + 2HI and 2CI₂ → C₂ + 2I₂, respectively. The rate constants of these reactions were determined.     

Theoretical investigation on the geometries and electronic properties of cesium–silicon CsSi<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 2–12) clusters

The structures, relative stabilities, and electronic properties of pure Si _n and Cs-doped silicon clusters (n = 2–12) are systematically investigated using the density functional theory at the B3LYP level. The optimized structures indicated that the lowest-energy structures of CsSi _n are similar to those of pure Si _n clusters and prefer the 3-dimensional configuration for n = 3–12. The relative stabilities of CsSi _n clusters are analyzed based on the averaged binding energy, fragmentation energy, second-order energy difference, and HOMO–LUMO energy gap. It is found that CsSi₆ and CsSi₉ are the magic clusters, and the doping of Cs atom reduces the chemical stabilities of Si _n frame. The Mulliken population analysis pointed out that the charges in the corresponding CsSi _n clusters always transfer from Cs atom to Si _n host in the range of 0.80–0.91 electron. In addition, the partial density of states, infrared, and Raman spectra is discussed.     

Synthesis of Polyfluorinated Ethers

Procedures for preparing polyfluorinated ethers H(CF₂CF₂) _n CH₂OR by alkylation of the corresponding telomeric alcohols H(CF₂CF₂) _n CH₂OH (n = 1–3) with alkyl halides and alkyl tosylates were examined.     

Synthesis of Block Copolymers of Styrene with <Emphasis Type="Italic">D</Emphasis>,<Emphasis Type="Italic">L</Emphasis>-Lactide by the Sequential Controlled Cationic Polymerization and Ring-Opening Anionic Polymerization

The cationic polymerization of styrene initiated by the system 2-chloro-2-phenylpropane–TiCl₄–pyridine is studied in a mixture CH₂Cl₂–n-hexane at a temperature of –80°С. It is shown that under these conditions polymerization occurs via the living mechanism at [monomer]: [initiator] ≤ 100. The method of preparing polystyrenes with terminal primary hydroxyl groups (M_n = 4000–10000 g/mol) by the sequential controlled cationic polymerization of styrene and the in situ alkylation of 4-phenoxy-1-butanol by polystyrene macrocations is proposed. The resulting functionalized polystyrenes are used as macroinitiators of anionic-coordination ring-opening polymerization of D,L-lactide in the presence of tin bis(2-ethyl hexanoate) [Sn(Oct)₂] in toluene at 80°С. Copolymers polystyrene-block-poly(D,L-lactide) with the controlled length of the poly(D,L-lactide) block (M_n = 10000–17000 g/mol) and a relatively low molecular-weight distribution (M_w/M_n = 1.6–1.8) are synthesized. Formation of the block copolymers is confirmed by ¹Н NMR spectroscopy, gel-permeation chromatography, and atomic force microscopy.     

First principle study of magnetic and electronic properties of single X (X = Al,Si) atom added to small carbon clusters (C<Subscript> <Emphasis Type="Italic">n</Emphasis> </Subscript>X, <Emphasis Type="Italic">n</Emphasis> = 2–10)

In this paper, the magnetic and electronic properties of single aluminum and silicon atom added to small carbon clusters (C_nX; X = Al, Si; n = 2–10) are studied in the framework of generalized-gradient approximation using density functional theory. The calculations were performed for linear, two dimensional and three dimensional clusters based on full-potential local-orbital (FPLO) method. The total energies, HOMO–LUMO energy gap and total magnetic moments of the most stable structures are presented in this work. The calculations show that C_nSi clusters have more stability compared to C_nAl clusters. In addition, our magnetic calculations were shown that the C_nAl isomers are magnetic objects whereas C_nSi clusters are nonmagnetic objects.     

Special Features of the Interaction between Asymmetric Dimethylhydrazine and Thiocontaining Schungite

The interaction between asymmetric dimethylhydrazine and thiocontaining mineral schungite-III has been studied. Chromatography–mass spectrometry has been used to identify alkyl polysulfides as the products of desorption of asymmetric dimethylhydrazine from schungite surface. The interaction of asymmetric dimethylhydrazine with crystalline sulfur has been investigated in a model system. Dimethyl polysulfides, CH₃S_nCH₃; (dimethylamino)methyl polysulfides, (CH₃)₂NS_nCH₃; and bis(dimethylamino) polysulfides, (CH₃)₂NS_nN(CH₃)₂, with 2 ≤ n ≤ 4 have been detected. Gas-chromatographic retention indices have been determined for the products of the interaction of asymmetric dimethylhydrazine with sulfur and the schungite material.     

DFT study of small aluminum and boron hydrides: isomeric composition and physical properties

The structure, energetics, and physical properties, including rotational constants, characteristic vibrational temperatures, dipole moment, static polarizability, HOMO-LUMO gap, formation enthalpy and collision diameter of different isomeric forms of atomic Al _n H _m and B _n H _m clusters with n = 1..4 and all feasible m numbers are studied within the density functional theory framework. The search of isomer structures has been accomplished using multistep hierarchical algorithm. Temperature dependences of thermodynamic functions (enthalpy, entropy and specific heat capacity) have been calculated both for the individual isomers and for the ensemble of isomers with equilibrium composition for each class of clusters, taking into account the anharmonicity of cluster vibrations and the contribution of excited electronic states. The prospects of the application of small atomic Al _n H _m and B _n H _m clusters as the components of energetic and hydrogen storage materials are also discussed.     

Electronic structure and excited states of molecular crystals of antimony and tellurium hexahalogenides

The article examines the electronic structure and orbital nature of luminescence excitation in a series of molecular crystals with the general formula E _n AX₆, where E _n are organic and inorganic cations (diphenylguanidinium, guanidinium, and cesium); n is the number of cations; AX₆ are Te(IV) and Sb(III) anions; X are the atoms of halogens Cl or Br. The electronic structure of these molecular crystals is determined from the data of X–ray photoelectron spectroscopy of the core and valence levels and еру quantum chemical modeling фе the density functional theory level together with the previously obtained single crystal X–ray diffraction data.     

Synthesis and structure of Pt(II) acetamidate complexes containing <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethyl-substituted ethylenediamine and trimethylenediamine

Reactions of acetamide with platinum(II) diamines [Pt(N,N-DimeEn)Cl₂], [Pt(Tm)Cl₂], and [Pt(N,N-DimeTm)Cl₂] (N,N-DimeEn = (CH₃)₂N(CH₂)₂NH₂, Tm = NH₂(CH₂)₃NH₂, N,N-DimeTm = (CH₃)₂N(CH₂)₃NH₂) with preliminary precipitation of chlorine ions by silver salts gave binuclear Pt(II) acetamidates [Pt₂(CH₃)₂N(CH₂)₂NH₂)₂(μ-NHCOCH₃)₂](NO₃)₂ · H₂O (I), [Pt₂(NH₂(CH₂)₃NH₂)₂)(μ-NHCOCH₃)₂](NO₃)₂ · H₂O (II), and [Pt₂(CH₃)₂N(CH₂)₃NH₂)₂(μ-NHCOCH₃)₂](HSO₄)₂ (III), whose crystal structures were determined. Crystals of I are monoclinic: a = 14.459(2) Å, b = 17.197(3) Å, c = 9.822(2) Å, β = 105.923(10)°, V = 3348.6(8) ų, space group P2(1)/c, Z = 4, R _hkl = 0.0419 for 6663 reflections. Complex I is a binuclear acetamidate with bridging (NHCOCH₃)^? ligands, one of which is bound to two Pt atoms through the N and O atoms, and the other ligand is bound only through the N atom. The Pt-Pt distance is 2.987(1) Å. Crystals of II are monoclinic: a = 10.213(7) Å, b = 13.373(9) Å, c = 16.533(11) Å, β = 97.971(9)°, V = 2236(3) ų, space group P2(1)/n, Z = 4, R _hkl = 0.557 for 6462 reflections. The Pt-Pt distance is 3.057(1) Å. Crystals of III are monoclinic: a = 10.557(12) Å, b = 18.531(2) Å, c = 14.4744(17) Å, β = 108.705(2)°, V = 2682(5) ų, space group P2(1)/n, Z = 4, R _hkl = 0.569 for 8506 reflections. The Pt-Pt distance is 3.202(1) Å. Complexes II and III are binuclear acetamidates, in which two chelating Pt(Tm) or Pt(N,N-DimeTm) moieties are coordinated through the N and O atoms of (NHCOCH₃)^? cis-bridges.     

Photo-dehydrogenation of 4,6-diaryl-2-oxo-1,2,3,4-tetrahydropyrimidines

Electron-transfer-induced photo-oxidation of 4,6-diaryl-substituted 2-oxo-1,2,3,4-tetrahydropyrimidines (THPMs) in chloroform under argon atmosphere results in the smooth formation of 4,6-diaryl-substituted 2-oxo-1,2-dihydropyrimidines. Sequentially, electron-transfer and proton removal processes in this oxidative reaction result in the occurrence of two different benzylic and allylic radical intermediates, which converted to each other via resonance. Preferably, capto-dative stabilized radical center stimulates the type of product. Based on the proposed oxidation reaction mechanism, the electron transfer from the excited THPMs to chloroform starts this oxidative reaction. The results of the computational study obtained at DFT-B₃LYP/6-311++G** level of theory indicate that the first electron is preferably removed from the N₁ atom of the heterocyclic ring. A comparison of the sum of the Mulliken spin densities of the radical intermediates supports the argument that the more stable capto-dative stabilized radical is involved in the reaction.     

Crystal Structure of [UO<Subscript>2</Subscript>SO<Subscript>4</Subscript>{(CH<Subscript>3</Subscript>)HNCONH(CH<Subscript>3</Subscript>)}<Subscript>2</Subscript>]

The single crystals of [UO₂SO₄{(CH₃)HNCONH(CH₃)}₂] (I) were synthesized and studied by X-ray diffraction. The crystals are monoclinic, a = 6.847(1) Å, b = 14.259(3) Å, c = 14.297(3) Å, β = 93.451(4)°, space group P2₁/n, Z = 4. The main structural units of crystals I are ribbons whose composition coincides with the composition of the compound. The crystal chemical formula of the complex is AT³M ₂ ¹ (A = UO ₂ ²⁺ ).     

New carborane-containing acids and amines

Alkylation of nido-carborane methyl sulfide derivative [9-MeS-7,8-C₂B₉H₁₁]^– was used to synthesize a series of new carborane-containing acids 9-HOOC(CH₂) _n (Me)S-7,8-C₂B₉H₁₁ (n = 1—4) and amines 9-H₂N(CH₂) _n (Me)S-7,8-C₂B₉H₁₁ (n = 2, 3). The compounds obtained can be used for the development of BNCT agents.