Comparison of the capacity of nitrogen, oxygen, sulfur, and selenium atoms to exist in onium states. quantum-chemical investigation of isomeric model systems with two heteroatoms

HF, B3LYP, and MP2 calculations with the 6-31+G(d) basis set with correction to the energy of zero-point vibrations were carried out to determine the energy characteristics of model molecules containing two heteroatoms in the sp ³- and sp ²-hybrid states; different combinations of N, O, S, and Se atoms were studied. The stability of the onium states of the nitrogen atom was found to be greater than for its chalcogen analogs and the relative stability of onium states of the chalcogen analogs was found to depend on the hybridization of these atoms. Analysis of these results permitted us to construct a stability series of onium derivatives and to interpret the positional selectivity in electrophilic substitution reactions of five-membered heterocyclic compounds with one heteroatom. To J. Stradins, an outstanding and tireless scientist, with our deep respect and sincere affection. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1801–1808, December, 2008.     

Geminal interactions in ClZ(CH3)2X molecules (Z = C, Si, Ge) according to ab initio calculations

The structure and electronic parameters of ClZ(CH₃)₂X molecules (Z = C, Si, Ge, X = CH₃, OCH₃) were calculated by the RHF/6–31G(d) and RHF/6–311G(d,p) methods with full geometry optimization; calculations of ClZ(CH₃)₂OCH₃ molecules were also performed by the RHF/6–31G(d) method with partial geometry optimization. The ³⁵Cl NQR frequencies calculated from the populations of less diffuse 3p constituents of valence p orbitals of chlorine [RHF/6–31G(d)] were in agreement with the experimental values. The ³⁵Cl NQR frequencies for molecules with X = OCH₃ are lower than those for molecules with X = CH₃ (the Z atom being the same), due mainly to direct through-field polarization of the Z-Cl bond, induced by the effect of unshared electron pair of the oxygen atom in the trans position with respect to that bond. The difference in the ³⁵Cl NQR frequencies decreases in going from Z = C to Z = Si, Ge, in parallel with variation of the Z-Cl bond polarization as the size of Z increases.     

Ab initio Mechanism Study on the Reaction of Chlorine Atom with Formic Acid

The potential energy surface(PES) for the reaction of Cl atom with HCOOH is predicted using ab initio molecular orbital calculation methods at UQCIDS(T,full)6-311 G(3df,2p)//UMP2(full)/6-311 G(d,P) level of theory with zero-point vibrational energy (ZPVE) correction.The calculated results show that the reaction mechanism of Cl atom with formic acid is a C-site hydrogen abstraction reaction from cis-HOC(H)O molecule by Cl atom with a 3.73kJ/mol reaction barrier height,leading to the formation of cis-HOCO radical which will reacts with Cl atom or other molecules in such a reaction system.Because the reaction barrier height of O-site hydrogen abstraction reaction from cis-HOC(H)O molecule by Cl atom which leads to the formation of HCO2 radical is 67.95kJ/mol,it is a secondary reaction channel in experiment,This is in good agreement with the prediction based on the previous experiments.     

An investigation on the reaction mechanism of the F2+Cl2→2ClF using the B3LYP method

The reaction mechanism of F₂+Cl₂→2ClF has been investigated with the density functional theory at the B3LYP/6‐311G* level. Six transition states have been found for the three possible reaction paths and verified by the normal mode vibrational and IRC analyses. Ab initio MP2/6‐311G* geometry optimizations and CCSD(T)/6‐311G(2df)//MP2/6‐311G* single‐point energy calculations have been performed for comparison. It is found that when the F₂ (or Cl₂) molecule decomposes into atoms first and then the F (or Cl) atom reacts with the molecule Cl₂ (or F₂) nearly along the molecular axis, the energy barrier is very low. The calculated energy barrier of F attacking Cl₂ is zero and that of Cl attacking F₂ is only 15.57 kJ?mol^?1 at the B3LYP level. However, the calculated dissociation energies of F₂ and Cl₂ are as high as 145.40 and 192.48 kJ?mol^?1, respectively. When the reaction proceeds through a bimolecular reaction mechanism, two four‐center transition states are obtained and the lower energy barrier is 218.69 kJ?mol^?1. Therefore, the title reaction F₂+Cl₂→2ClF is most probably initiated from the atomization of the F₂ molecule and terminated by the reaction of F attacking Cl₂ nearly along the Cl? Cl bond. MP2 calculations lead to the same conclusion, but the geometry of TS and the energy barrier are somewhat different. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002     

Free radical abstraction of H atom from peroxides with concerted dissociation of O-O bond

Quantum chemical calculations of the dissociation energy of the C-H bond in the ??-hydroperoxide fragment of Me₂CHOOH were carried out. It was shown that abstraction of H atom is accompanied by dissociation of the O-O bond. Density functional calculations of transition states of the reactions of ^·CH₃, CH₃OO^·, and HO₂ ^· radicals with the C-H bond in the ??-hydroperoxide fragment of Me₂CHOOH were carried out. It was established that H atom abstraction is accompanied by concerted dissociation of the O-O bond. For 45 peroxides R¹R²CHOOH, R¹R²CHOOR³, and R¹R²CHOOC(O)R³ (R¹, R² = H, Me, Et, Ph, H₂C=CH), the enthalpies of H atom abstraction from the C-H bond in the a-hydroperoxide fragment with fragmentation of the peroxides at the O-O bond were calculated. The kinetic parameters for 12 classes of radical abstraction reactions with fragmentation of molecules were calculated from experimental data within the framework of the model of intersecting parabolas. The activation energies and reaction rate constants of H atom abstraction from C-H bonds of a-peroxide fragments involving peroxyl and alkyl radicals were determined for 45 peroxides of different structure.     

Concerted stereodynamics of chemical changes: The branching selectivity in the photodissociation of asymmetric-top molecules,formic acid,and the cold reactivity of the H + H2 exchange reaction

This review article presents our recent examples of the branching selectivity in the photodissociation of asymmetric-top molecules, halothane CF₃CHBrCl and isohaloethane CF₂BrCHFCl. The former gave the unexpected branching ratio of ([Cl] + [Cl*])/([Br] + [Br*])$\approx$2 for the Br, Br* and Cl, Cl* atom fragmentations, meaning that the strongly bounded Cl-C bond gave twice favorable fragmentation, while the later isohaloethane gave almost the same value for all-atom fragmentations. We interpret this result due to the curve crossing of electronically excited states and the non-adiabatic interaction on the excited states. The bimodal vibrational distribution of the product CO fragment in the formic acid photodissociation at 193 nm evidenced a roaming signature by using the μs time-resolved Fourier-transform infrared emission spectra for the first time. We find the characteristic propensity rule in the time-dependent interaction potential to judge reactivity in the H + H₂ exchange reaction and the roaming-type of trajectory at temperature 3 K, by use of the impact-parameter dependent quasi-classical trajectory simulation, based on the present results, we conclude that reaction dynamics proceeds not only by the prerequisite of energy conservation but also by the timing of the time-dependent interaction potential which is very sensitive to the steric configuration of reaction intermediate, thus it may be called as the concerted stereodynamics.     

Theoretical study on the kinetics and branching ratios of the gas phase reactions of 1, 1-Dichlorodimethylether (DCDME) with Cl atom

Quantum mechanical calculations are carried out on the reactions of CH₃OCHCl₂ (DCDME) with Cl atom by means of DFT and couple cluster methods. The geometries of the reactants, products, and transition states involved in the reaction pathways are optimized at BHandHLYP level of theory using 6-311G(d,p) basis set. Transition states are searched on the potential energy surface involved during the reaction channels, and each of the transition states is characterized by the presence of only one imaginary frequency. The existence of transition states on the corresponding potential energy surface is ascertained by performing intrinsic reaction coordinate calculation. Single point energy calculations are performed at CCSD(T) level using the same basis set. The hydrogen abstraction rate constant for the title reaction is calculated at 298 K and atmospheric pressure using the canonical transition state theory including tunneling correction. The calculated value for rate constant as 1.204 × 10^?12 cm³ molecule^?1 s^?1 is found to be in very good agreement with the recent experimental data. The percentage contributions of both reaction channels are also reported at 298 K.     

Cu(II) and Cu(I) complexes with 2-(3,5-diphenyl-1H-pyrazole-1-yl)-4,6-diphenylpyrimidine: Synthesis and structure. Catalytic activity of Cu(II) compounds in reaction of ethylene polymerization

The Cu(II) and Cu(I) complexes with 2-(3,5-diphenyl-1H-pyrazole-1-yl)-4,6-diphenylpyrimidine (L) of the composition CuLX₂ (X = Cl, Br) and CuL(MeCN)Br are synthesized. According to X-ray diffraction data, the complexes have molecular structures. The molecules L are coordinated to the copper atom in bidentate-cyclic mode, i.e., through the N² atom of pyrazole and N¹ atom of pyrimidine rings. The coordination polyhedron of the Cu²⁺ ion in CuLX₂ compounds is completed to a distorted tetrahedron with halide ions, that of the Cu⁺ ion in CuL(MeCN)Br compounds, with the bromide ion and the nitrogen atom of acetonitrile molecule. The CuLX₂ complexes (X = Cl, Br) in combination with cocatalysts (methylaluminoxane and triisobutylaluminium) exhibit catalytic activity in ethylene polymerization.     

Remarkable Differences in Amine Substitution Reactions of Trichloromethyl and Trifluoromethyl Difluorophosphines,CX3PF2 (X = F,Cl): A Computational Study

Detailed computational studies have been carried out to explain the unexpected differing reactions that occur between dimethylamine and the difluorophosphines, CX₃PF₂ (X = F, Cl). The reaction affords the thermodynamically controlled product chloroform in the case of X = Cl, whereas when X = F the analogous reaction pathway leading to fluoroform is hindered by a substantial reaction barrier in the gas phase, where the reaction should take place due to the volatility of the reactant. While the gas‐phase reaction energy gap is somewhat reduced when X = Cl, due to the stability of the migrating CCl₃⁻ moiety, the still substantial barrier does not account for the chloroform formation. Polarizable continuum model (PCM) calculations indicate a reduction of the barrier, facilitating the liquid‐phase reaction. The alternative gas‐phase reaction path, resulting in the aminolysis of a P—F bond is reversible and is shifted toward the product by capturing HF as the dimethylamino salt of the [CF₃PF₄H]⁻ anion.     

Vacant outer orbitals in oxy anions of silicon,phosphorus, sulfur,and chlorine

The ions MO₄ ^n–, where M = Si, P, S, and Cl, have been calculated by a nonempirical Hartree-Fock method with the inclusion of the vacant 3d and 4s AO's of the central atom in the basis set. The calculations have shown that an increase in the role of the vacant outer molecules in M-O chemical bonding occurs.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 26, No. 2, pp. 233–236, March–April, 1990.     

Quantum-chemical investigation of the electrophile affinity of molecules of five-membered heterocycles with one hetero-atom and some model systems

Quantum-chemical calculations have been made of the energy characteristics of the molecules of pyrrole, furan, thiophene, and selenophene, the simplest derivatives of N, O, S, and Se with sp³-and sp²-hybridized C atoms and heteroatoms, and also of the products of addition of proton and certain other electrophiles to these molecules. The calculations were carried out by HF, B3LYP, and MP2 methods with the 6−31+G(d) basis set with corrections to the energy of zero-point vibrations. It was shown that the values of the affinity of the nitrogen-containing systems towards the electrophile were significantly greater than for their analogs, derivatives of chalcogens, while the relative stability of the onium states of the latter depends both on the hybridization of the heteroatoms, and also on the nature of the electrophile. Analysis of the obtained results made it possible to build a stability series of the onium compounds and to interpret the special features of the positional selectivity in electrophilic substitution reactions of five-membered heteroaromatic compounds with one heteroatom. Dedicated to the remarkable heterocyclic chemist Aleksandr Fedorovich Pozharskii on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1645–1654, November, 2008.     

Effect of steric strains in the macroring on the structure and properties of molecular complexes of (chloro)[5,15-(p-butoxyphenyl)-2,8,12,17-tetramethyl-3,7,13,17-tetrabutylporphinato]aluminum

The chelate (Cl)AlP was prepared by complexation of porphine (P) with aluminum(III) chloride in refluxing pyridine. Equilibrium coordination of nitrogen-containing ligands (L = 2-methylimidazole, imidazole, pyridine, 3,5-dimethylpyrazole, dimethylformamide) with (Cl)AlP in benzene was studied by spectrophotometric titration and computer simulation. Quantitative and qualitative characteristics of the reaction were obtained. The structure of the mixed-ligand complex formed by intermolecular interaction of the metal porphyrin with a base was determined spectrophotometrically and by quantum-chemical calculations. An effect of additional molecular ligand and of steric strain in the macroring on the stability of the complex was noted. The stability constant (K _s) increases with an increase in the basicity (K _BH ⁺) of the extra ligand and is proportional to the shift of the main bands (?λ) in the electronic absorption spectra. The geometric and energy characteristics of hexacoordinated aluminum porphyrin were calculated by the PM3 method. Correlations were found between the calculated energy of the interaction of the aluminum atom with the base molecule (E _b) and stability of the mixed-ligand complexes (Cl)Al(L)P. The cis and trans effects in the complexes (Cl)Al(L)P were analyzed. The dependence of the strength of the Al-L bond on the nature of the porphyrin and the basicity of the additional molecular ligand was determined from the experimental data and calculation results.     

Energy disposal in gas-phase nucleophilic displacement reactions

The partitioning of reaction exothermicity into relative translational energy of the products of gas-phase S_N2 (F^? + CH₃Cl) and nucleophilic aromatic substitution (F^? + C₆H₅Cl) reactions has been investigated using kinetic energy release Fourier transform ion cyclotron resonance spectroscopy. The chloride product ion is observed to be highly translationally excited for the S_N2 reaction, indicating a cold internal energy distribution for the products. For the chlorobenzene reaction the products are not generated with large translational energies. The results are compared with a statistical model. Ion-intensity profiles for the CH₃Cl reaction deviate significantly from the statistical model whereas the chlorobenzene results are consistent with this model. The kinetic energy release for the CH₃C1 reaction is compared with energy-disposal results for the photodissociation and dissociative electron-attachment processes of halomethanes. In all three cases a node in the molecular orbital between the carbon atom and the departing halogen results in a repulsive energy release. Ion-retention curves for the nucleophilic aromatic substitution reaction are consistent with the existence of a long-lived ion-dipole complex on the exit channel for this reaction.     

Synthesis, Spectroscopic Properties and Crystal Structures of Dibenzyltin（IV） Dithiobenzoate and Chlorodibenzyltin（IV） Thiobenzoate

Two dibenzyltin(IV) complexes with thiobenzoate ligand, (PhCH2)2Sn(SOCPh)2 (1) and (PhCH2)2Sn(C1)SOCPh (2), have been synthesized by the reaction of dibenzyltin(IV) dichloride with thiobenzoic acid in the presence of organic base Et3N and characterized by IR, ^1H NMR spectroscopy and elemental analysis. Their crystal structures were determined by X-ray single crystal diffraction analysis. In the crystals of 1, the tin atom is six-coordinated in a distorted octahedron configuration. In the crystals of 2, the molecular packing in unit cell reveals that the two adjacent molecules are symmetrically linked to each other to form a dimer with intermolecular Sn…C1 distances of 0.3591 (2) nm and the tin atom is five-coordinated in a distorted trigonal bipyramid configuration.     

5,15-bis(4′-methoxyphenyl)-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphin axial complexes of rhenium: Synthesis and reactions in protic solvents

The spectral (UV–Vis, IR, and NMR ¹H) properties and the state of oxorhenium(V) complexes with 5,15-bis(4′-methoxyphenyl)-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphin H₂P (O=Re(X)P) in protic solvents have been studied depending on the axial trans-ligand X^– (X = Cl, OPh, or OH). The O=Re(Cl)P, O=Re(OPh)P, and O=Re(OH)P in AcOH and CF3COOH are subjected to reaction of substitution their axial ligands with solvent molecules or anions, while remaining stable to the dissociation of M–N bonds and to oxidation both to the macrocyclic ligand and to the central metal cation. Quantitative parameters of the coordination of molecular oxygen by O=Re(Cl)P in 17.4–18.2 M H₂SO₄ to form O=Re(O₂)P⁺ · Cl^– have been obtained, these parameters being independent of the initial H₂SO₄ concentration. The character of peripheral functional substituents in H₂P has been shown to be responsible for the stability of the studied oxo complexes to chemical oxidation in aerated acids.     

Mechanism and kinetics of the reaction of ozone with sodium chloride in aqueous solutions

It is shown experimentally that Cl⁻ appreciably accelerates ozone decomposition in water (τ_1/2 = 1.5 h versus 6 h in pure water). The decomposition of ozone in NaCl solutions includes the reversible reaction of ozone with the chloride ion (O₃ + Cl⁻ → O₃⁻ + Cl) as the key step, which is followed by the development of a chain reaction in which chain propagation is performed alternately by the chlorine atom Cl and its monoxide ClO. The current concentrations of the chlorine atom are rather low ([Cl] ∼ 10⁻¹⁴ mol/l). The overall process is satisfactorily described by a first-order rate law with respect to ozone. The decomposition of ozone in aqueous solutions of NaCl is not accompanied by the formation of products other than oxygen. In particular, no noticeable amounts of hypochlorites and chlorates are observed. This is particularly significant for medicinal applications of ozonized isotonic solutions.     

Ab initio calculations of chloride complexes of Au, Hg, Tl, Pb, and Bi in anomalous oxidation states (2S1/2 electron state)

Ab initio calculations of chloride complexes of Au, Hg, Tl, Pb, and Bi in anomalous oxidation states (²S_1/2 electron state) were carried out by the Becke-Lee-Yang-Parr density functional method using the Dunning-Hay LanL2DZ basis set. Optimum geometric parameters and electronic characteristics of MCl _n (H₂O) _m ⁿ (n=1–4 andm=0,4,5) complexes were determined. In each of the considered series the spin, population on the central metal atom decreases as its atomic number increases. The energy of transition of the unpaired electron to the lowest unoccupied MO decreases in the same order. The unpaired electron occupies an orbital that is mostly a linear combination of the s-orbital of the metal atom and the p-orbital of the Cl atom (the antibonding σ-orbital of the M−Cl bond). Distinctions in the changes in spectral properties of aquacomplexes and chloride complexes in isoelectronic series, observed as the degree of oxidation of the metal atom increases, were explained. The results of calculations are in agreement with the experimental data obtained by ESR and optical spectroscopy. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1049–1055, June, 1999.     

The α‐effect exhibited in gas‐phase SN2@N and SN2@C reactions

In order to explore the existence of α‐effect in gas‐phase S_N2@N reactions, and to compare its similarity and difference with its counterpart in S_N2@C reactions, we have carried out a theoretical study on the reactivity of six α‐oxy‐Nus (FO^?, ClO^?, BrO^?, HOO^?, HSO^?, H₂NO^?) in the S_N2 reactions toward NR₂Cl (R = H, Me) and RCl (R = Me, i‐Pr) using the G2(+)_M theory. An enhanced reactivity induced by the α‐atom is found in all examined systems. The magnitude of the α‐effect in the reactions of NR₂Cl (R = H, Me) is generally smaller than that in the corresponding S_N2 reaction, but their variation trend with the identity of α‐atom is very similar. The origin of the α‐effect of the S_N2@N reactions is discussed in terms of activation strain analysis and thermodynamic analysis, indicating that the α‐effect in the S_N2@N reactions largely arises from transition state stabilization, and the “hyper‐reactivity” of these α‐Nus is also accompanied by an enhanced thermodynamic stability of products from the n_(N) → σ*_(O?Y) negative hyperconjugation. Meanwhile, it is found that the reactivity of oxy‐Nus in the S_N2 reactions toward NMe₂Cl is lower than toward i‐PrCl, which is different from previous experiments, that is, the S_N2 reactions of NH₂Cl is more facile than MeCl. © 2013 Wiley Periodicals, Inc.     

Magnesiumphthalocyanine: Darstellung und Eigenschaften von Halogenophthalocyaninatomagnesat, [Mg(X)Pc2−]− (X = F,Cl, Br); Kristallstruktur von Bis(triphenylphosphin)iminiumchloro(phthalocyaninato)magnesat-Aceton-Solvat

Magnesium Phthalocyanines: Synthesis and Properties of Halophthalocyaninatomagnesate, [Mg(X)Pc^2?]^? (X = F, Cl, Br); Crystal Structure of Bis(triphenylphosphine)iminiumchloro-(phthalocyaninato)magnesate Acetone Solvate Magnesium phthalocyanine reacts with excess tetra(n-butyl)ammonium- or bis(triphenylphosphine)iminiumhalide ((ⁿBu₄N)X or (PNP)X; X = F, Cl, Br) yielding halophthalocyaninatomagnesate ([Mg(X)Pc^2?]^?; X = F, Cl, Br), which crystallizes in part as a scarcely soluble (ⁿBu₄N) or (PNP) complex-salt. Single-crystal X-ray diffraction analysis of ^b(PNP)[Mg(Cl)Pc^2?] · CH₃COCH₃ reveals that the Mg atom has a tetragonal pyramidal coordination geometry with the Mg atom displaced out of the center (Ct) of the inner nitrogen atoms (N_iso) of the nonplanar Pc ligand toward the Cl atom (d(Mg? Ct) = 0.572(3) Å; d(Mg? Cl) = 2.367(2) Å). The average Mg? N_iso distance is 2.058 Å. Pairs of partially overlapping anions are present. The cation adopts a bent conformation (^b(PNP)⁺: d(P1? N(K)) = 1.568(3) Å; d(P2? N(K)) = 1.587(3) Å; ?(P1? N(K)? P2) = 141.3(2)°). Electrochemical and spectroscopic properties are discussed.     

Substrate and positional selectivity in electrophilic substitution reactions in pyrrole, furan, thiophene, and selenophene derivatives and related benzoannelated systems

Data on the relative reactivities (substrate selectivity) of five-membered heterocycles in electrophilic substitution reactions and positional selectivity (α : β ratio) in these reactions were analyzed. Unlike the substrate selectivity (pyrrole ≫ furan > selenophene > thiophene) determined by the position of heteroatoms in the Periodic Table, the positional selectivity decreases in the order corresponding to the change in the relative stability of the onium states of the elements (O⁺ < Se⁺ ≤ S⁺ < N⁺) and reflects the predominant role of heteroatoms in the stabilization of σ complexes formed upon β-substitution. These differences in the positional selectivity of the parent heterocycles have a substantial effect on the orientation in electrophilic substitution reactions in their derivatives and the corresponding benzoannelated systems. This interpretation was confirmed by ab initio quantum chemical calculations (RHF/6–31G(d) and MP2/6– 31G(d)//RHF/6–31G(d)) and density functional theory calculations (B3LYP/6–31G(d)). Quantum chemical calculations were performed by the above-mentioned methods for model N-R-pyrroles (R = Me, Et, Prⁱ, Bu^t, CH=CH₂, C≡CH, Ph, PhSO₂, and 4-O₂NC₆H₄) and their α- and β-protonated σ complexes. The results of these calculations demonstrated that it is the steric factors and charges on the β-C, α-C, and N atoms and the substituents at the N atom (the kinetic control), as well as the nature of the electrophile, rather than the difference in the relative stabilities of the onium states of N⁺ (which depends on the nature of the substituent at the N atom and reflects the role of the heteroatom in stabilization of σ complexes formed via β-substitution; the thermodynamic control) that are responsible for the type of orientation (α or β) that prevails. Dedicated to Academician V. I. Minkin on the occasion of his 70th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 837–846, April, 2005.