Reactions of Peroxy Radicals with Hydrocarbons and Alcohols: Transition State Geometry and the Polar Effect

The reaction EtOO + EtH EtOOH + Et was studied by the intersecting parabolas method and calculated using density functional theory. The interatomic C–H, O–H, and C–O distances of the transition state for this reaction were calculated using these methods. The formulas for calculating these distances from experimental data were obtained. Similar calculations and comparisons were carried out for the reaction EtOO + MeCH₂OH EtOOH + MeCHOH. The polar effect of the hydroxy groups on the transition state manifested itself in a decrease in the activation energy and in the formation of a nonlinear structure of the transition state. An empirical formula for estimating the C–H–O angle in the transition state from the enthalpy and activation energy was derived.     

Ab initio calculations of potential energy surface for reaction of nucleophilic addition of H− ion to methylacetylene

Within the framework of the Hartree-Fock-Roothaan Method, using double- basis sets 3-21++G and (6-31-H-G//3-21++G), the minimum energy paths (MEPs) have been calculated for reactions of nucleophilic addition of the hydride ion H^– to the methylacetylene molecule: CH₃-CCH+H^–[CH₃-CH=CH]^– (1) CH₃-CCH+H^–[CH₃-C=CH₂]^– (2). It has been established that the activation energy for reaction (2) is 7.02 kJ/mole lower than for reaction (1). An analysis has been made of the character of electron density distribution along the MEP of each reaction. It has been shown that distortion of geometry of the reactants plays an important role in intensifying the interaction of the frontier orbitals. The reasons for nonfulfillment of Markownikoff's rule for these reactions have been determined. The results from the calculations are compared with calculations reported in the literature for the related reaction of nucleophilic addition of the hydride ion H^– to the acetylene molecule: HCCH+H^–[CH₂=CH]^–.Translated from Teoreticheskaya i Éxperimental'naya Khimiya, Vol. 21, No. 3, pp. 303–309, May–June, 1985.     

Calculation of low-lying electronic states of the MgN molecule in the effective-core-potential approximation

Plots of the potential energy and the dipole moment of four low-lying electronic states of the MgN molecule have been calculated by the self-consistent-field and configuration-interaction methods in the effective-core-potential approximation. The ground state of the molecule is not bound and has^4– symmetry. The lowest bound states,² and^2–, are practically degenerate; the values of the equilibrium internuclear distances (1.91 and 1.98 Å) and the vibrational constants (637 and 519 cm^–1, respectively) have been found for them. The vertical energy of the transition from these states to the ground state amounts to about 0.5 eV.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 2, pp. 217–220, March–April, 1985.     

IR-Untersuchungen an B-Tris (dimethylamino) boroxin und B-Tris[dimethylamino (d6)] boroxin

Zusammenfassung In B-Tri(dimethylamino)boroxin zeigt — im Gegensatz zum B-Trimethoxyboroxin — die B–O-Hauptbande nur geringe Kopplung mit CH₃-Deformationsschwingungen. Die B–N-Valenzbande tritt hingegen mit _sCH₃ in Wechselwirkung, wodurch Banden mit gemischtem Schwingungscharakter entstehen. In der deuterierten Verbindung liegt BN verkoppelt mit BO bei 1461 cm^–1

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In B-Tri(dimethylamino)boroxin coupling between the B–O ring stretching main-band and CH₃ is weak in contrast to B-trimethoxyboroxine. Interference between BN and CH₃ leads to bands of mixed character, one of them is above 1500 cm^–1. In [(CD₃)₂NBO] BN coupled with BO is at 1461 cm^–1.

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Mit 2 Abbildungen     

Transfer Reactions of Rydberg (Quasi-Rydberg Molecular) Electrons in Condensed Media: IV. Large Proton Displacements upon Phosphorescence Quenching via Highly Excited Triplet States T* of Substituted Aromatic Solute Molecules in Solutions at 77 K

Intramolecular phosphorescence quenching via states T* in aromatic solute molecules containing N–H (diphenylamine (DPA) or carbazole), O–H (naphthol), etc. bonds was observed in methylcyclohexane at 77 K. The quantum yield of quenching measured for DPA increases with increasing the energy of the T* state. As in the case of external electron acceptors, the quenching and photodissociation are associated with the capture of excited * electrons onto polarized bonds N–H⁺, O–H⁺and with the formation of triplet complexes (for example, Ph₂N···H*, where H* is the excited hydrogen atom). The complexes can be deactivated via configurations with large proton displacement distances (Ph₂N^–···H⁺).     

Ab initio MP2 calculations of the products of acetylene addition to HgCl2

Gas-phase reaction of acetylene with HgCl₂ resulting in -chlorovinylmercury derivatives and their interaction with Cl^– and I^– anions and KI molecule was studied by the ab initio MP2 method with the Dunning—Hay double zeta basis set and LanL pseudopotential for Hg, K, and I atoms. The reaction was shown to proceed via a -complex of acetylene and HgCl₂ (the calculated enthalpy of formation is –6.5 kcal mol^–1). According to calculations, the activation energy of formation of cis--chlorovinylmercury chloride from acetylene and HgCl₂ is 31 kcal mol^–1. Chloride and iodide anions and KI molecule are readily added to both cis- and trans-isomer of -chlorovinylmercury chloride to give stable species.     

Electronic structure and the unimolecular reactions of imine peroixde HNOO

Summary Electronic structure and possible unimolecular reaction paths of a linear four-atom molecule HNOO to be formed by the addition of NH(^3–) toward O₂(³ _g ^– ) are investigated by the SCF and MRD-CI calculations employing the 6–31G** basis functions. HNOO in its ground state (¹ A) is an ozone-like diradicaloid, whose N–O binding energy is only 27 kJ/mol. Geometries and excitation energies of various diradical (excited) states, both singlet and triplet, are examined. The isomerization paths of the ground-state HNOO(¹ A) are traced by a multi-configuration (MC) SCF procedure and the activation barrier heights evaluated by the CI treatment. It has proved that energetically the most favorable is the 1,3-hydrogen migration to give hydroperoxynitrene NOOH(¹ A) with the barrier height of 62 kJ/mol. The nitrene should be extremely unstable; it is liable to be decomposed to NO + OH with virtually no activation barrier.Presented at the 7th International Congress on Quantum Chemistry, Menton, July 1991     

IR Study of p–π Conjugation in 2-Substituted 4-Methylene-1,3-dioxolanes and 4-Methyl-1,3-dioxoles

Selected group frequencies of the IR spectra of a number of 2-substituted 4-methylene-1,3-dioxolanes (a) and their endocyclic isomers, 2-substituted 4-methyl-1,3-dioxoles (b), have been studied to establish their usefulness as a measure of the strength of p– conjugation in the O—C=C moieties of the title compounds. In the exo compounds (a), the C=C stretching frequencies C=C and the in-phase, out-of-plane bending (wagging) frequencies CH₂ w of the =CH₂ group were found to be linearly related, besides to each other, also to the electron-donating character of the substituents and the ¹³C NMR chemical shift of the C atom of the exocyclic CH₂ group. This suggests that the two IR group frequencies of the exo isomers are linearly related to the strength of p– conjugation in the O—C=C moiety. The C=C stretching absorption of the exo compounds in the 1600–1700 cm^–1 region appeared as a doublet, shown to arise from Fermi resonance of the C=C fundamental with the CH₂ w overtone. The C=C frequencies of the endo compounds support some previous findings of an unexpected strength of p– conjugation in the 2-alkoxy derivatives. Finally, DFT calculations at the B3LYP/6-31G* level of theory are shown to give accurate predictions of the effect of 2-substituents on the group frequencies.     

Further investigations about the zwitterionic excited states of twisted conjugated molecules

For twisted zwitterionic excited states, the single-determinant closed-shell SCF approach favours one of the two possibly resonant structures A⁺B^– or A^–B⁺, but gives a very low energy by allowing reorganization and polarization under the field. This effect is very difficult to include in CI developments using neutral symmetry adapted MO's. The closed-shell SCF approach is always relevant for energy, and only fails for the wavefunction in the (near) degeneracy region between A^–B⁺ and A⁺ B^–, where the Born-Oppenheimer approximation, anyway, breaks down. The process is applied in nonempirical (minimal + diffuse AO basis set) calculations of butadiene. The role of geometry optimization and of further electron correlation is illustrated. The extent of polarization is shown in ethylene, suggesting a neutral two carbene limit picture of this excited state.     

Influence of chelating agents in eluent on the separation factor of lithium isotopes

The influence of chelating agents on the separation factor, , of lithium isotopes separation was studied by ion exchange elution chromatography. Eluents contained the chelating agent having different number of coordination sites. The chelating agents used in eluent were Na-glycine (Na–Gly), 2Na-iminodiacetic acid (2Na-IDA), 3Na-nitrilotriacetic acid (3Na-NTA), and 4Na-ethylenediaminetetraacetic acid (4Na-EDTA). The ion exchanger was Dowex 50W-X8, sulfonic acid type, sodium form. As a result,⁶Li was enriched in resin phase, and⁷Li was in solution phase. The separation factor, , was gradually increased with increasing number of coordination site (=1.0022–1.0038) at the same distribution coefficient and with increasing distribution coefficients (=1.0017–1.0026) at the same concentration of chelating agents.     

CEPA calculations on open-shell molecules. V. The vibration frequencies of SF and SCl

Ab initio calculations for the ² ground states of SF and SCl have been performed on Hartree-Fock level and with inclusion of valence shell correlation effects by means of the CI and CEPA approaches. The calculated properties are: Equilibrium distances, vibration frequencies, and dipole moment curves in the vicinity of the respective equilibrium geometries. Our best estimates for the 0 1 infrared absorption frequencies _o for SF and SCl are 786 cm^–1 and 520 cm^–1, respectively, both with an uncertainty of about 10 cm^–1. This confirms a recent experimental value obtained by Willner for SF (791 cm^–1), but indicates that for SCl both experimental values reported previously in the literature (617 cm^–1 and 574 cm^–1) are wrong. The S—F and S—Cl bonds in SF and SCl are very similar to the ones in SF₂ and SCl₂, being essentially single p-bonds in either case. In the analogous oxygen-halogen molecules the situation is different, the O—F and O—Cl bonds in the diatomic radicals OF and OCl have partial double bond character and are much stronger than those in OF₂ and OCl₂ or in HOF and HOCl.     

Mechanisms of Heterogeneous Processes in the System SiO2 + CH4: III. Products of >Si

Permenov  D. G.  Radzig  V. A. 《Kinetics and Catalysis》2004,45(2):273-278

Change of intensity of a1Δg → X3Σ g − transition in oxygen molecule upon interaction with H2, N2, and CS2

The semiempirical MINDO/3 CI method has been used to calculate collision complexes of the oxygen molecule with certain diamagnetic molecules, simulating the effect of solvents in increasing the intensity of the a¹_g X³ _g ^– transition in the oxygen molecule.Cherkassy Engineering Technology Institute, 460 Shevchenko Street, Cherkassy 257006, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 3, pp. 143–146, May–June, 1996. Original article submitted July 12, 1995.     

Spectroscopic manifestation of the accidental degeneracy of π=Δ electronic adiabatic terms of linear triatomic systems

The semiclassical form of the absorption band of a linear triatomic system which corresponds to an electronic transition from the -ground state term to the excited intersection and terms was calculated. The analysis was carried for negligibly small defect of frequencies and in the absence of a shift of the equilibrium position on excitation. The experimentally observed CuCl₂ absorption spectrum was interpreted qualitatively as a , gS transition on the existence of a point of = accidental degeneracy. The 7000–24000 cm^–1 energy interval in the spectrum was analyzed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 2, pp. 222–225, March–April, 1988.     

Relative reactivities of glycerophosphates towards permanganate in perchloric acid medium

Summary The reactivities of - and -glycerophosphates towards MnO ₄ ^– in HClO₄ medium have been examined. The reactions between glycerophosphates and MnO ₄ ^– are first order with respect to [glycerophosphate], [MnO ₄ ^– ] and [H⁺]. There is no evidence for cleavage of the C–O–P bond rather than the terminal –CH₂OH group being oxidized to the respective phosphoglyceraldehyde.     

Theoretical and Experimental Studies of the Nature of the Catalytic Activity of VO x /TiO2 Systems

The states of supported vanadium and the nature of activation of ammonia adsorbed on vanadium sites of V _x /Ti₂ catalysts are studied by ⁵¹V NMR spectroscopy and diffuse-reflectance IR Fourier-transform (DRIFT) spectroscopy using cluster quantum chemical calculations of N₃ adsorption. We employ the V _x /Ti₂ catalyst of two types: the monolayer catalyst in which vanadium is located on the surface of well-crystallized anatase and the catalyst in which vanadium embedded in the anatase lattice at a rather great depth. It is shown that ammonia is predominantly adsorbed on Lewis acid sites of the monolayer catalyst, whereas most of N₃ adsorbed on the catalyst containing bulk vanadium is in the form of ammonium ions. Analysis of experimental and calculated data suggests that, in the monolayer catalyst, N₃ molecules in the selective reduction of nitrogen oxides are activated on Lewis acid sites. Ammonia activation involves the dissociation of the N–H bond in a coordinated molecule, which results in the formation of the amide V–N₂ group and a water molecule coordinated by a V⁵⁺ ion. It is likely that, in the case of the catalyst containing bulk vanadium, this reaction occurs with the predominant participation of ammonium ions.     

Alkaline Hydrolysis of Nitroglycerin and Activation of Luminol Chemiluminescence

Alkaline hydrolysis of nitroglycerin (G) was studied using the chemiluminescent reaction of the hydrolysis products with 4-dimethylaminophthalhydrazide (L). The chemiluminescence kinetics follows the pseudo-unimolecular law, with the rate constant k ₁ proportional to [OH^–]. The apparent bimolecular constant k ₂ = k ₁/[OH^–] is equal to 0.021 l mol^–1 s^–1. The chemiluminescence quantum yield per one nitroglycerin molecule _G = (1.3 ± 0.3) × 10^–3 photons per one molecule ([G₀] [L]), and the reactant chemiluminescence quantum yield upon excitation by species X formed from G in the course of hydrolysis is (2.6 × 0.5) × 10^–2 photons per molecule ([G] [L₀]]). Hence, it follows that the hydrolysis of 100 nitroglycerin molecules results in about five X molecules exciting chemiluminescence. The effects of temperature, ionic strength, and composition of the solution on k ₂ were studied. Quantum-chemical calculation on the interaction of ^– ion with G molecule shows a possibility for peroxynitrite formation upon approach of the ion to the nitro group within the NO₂ plane. If the approach occurs not in the NO₂ plane, the conventional hydrolysis mechanism with substitution at nitrogen is realized.     

Acid–Base Zeta-Metric Titration of Quartz Dispersions in Ethanol Solutions of Electrolytes

The conductivity of dilute quartz suspensions and electrophoretic mobility of quartz particles in solutions with the concentration C = 10^–5–10^–2 M XBr (X = H, Cs, Na, and Li) and NaOH, as well as in mixed solutions of 10^–4 M XBr (X = Cs, Na, and Li) + 10^–4–10^–2 M HBr and 10^–4 M XBr + 10^–4–10^–2 M XOH (X = Cs, Na, and Li) in ethanol containing 6 vol % of water were measured using conductometry and microelectrophoresis. The values of surface conductivity of quartz were calculated by the Wagner formula and used to calculate zeta potential by the Henry–Booth formula. The resultant dependences (logC) suggest that the value and sign of zeta potential are determined not only by the adsorption of potential-determining ions ⁺ and ^–, but also by the competitive specific adsorption of all ions of the aforementioned electrolytes, the adsorption values increasing in a cation series Li⁺ < Na⁺ < Cs⁺ < H⁺ and an anion series Br^– < OH^–. In particular, it is found that the titration of the above suspensions with XOH bases results in the reversal of zeta potential sign from negative to positive at a concentration depending on the adsorption capacity of alkali cation.     

A Spectroscopic Study of an Anhydrous Tetraethyl Orthosilicate-Boric Acid-Ethanol System

Hydrolysis and condensation reactions in an anhydrous sol-gel system comprising tetraethyl orthosilicate (TEOS, Si(OC2H5)4), boric acid (H3BO3) and ethanol have been studied using X-ray diffraction and NMR spectroscopy, and similarities and differences with the more traditional aqueous system are discussed. Boric acid is able to hydrolyse TEOS directly, and subsequent condensation reactions form borosiloxane (=B–O–Si) and siloxane (Si–O–Si) linkages. In an aqueous system, borosiloxanes are unstable to hydrolysis and are formed only upon heat treatment of the gel, a restriction avoided with anhydrous conditions. The anhydrous mixture is stable indefinitely against gelation, but can be readily gelled by addition of NaOH in ethanol. This system may be useful for preparing borosilicate glasses at lower temperatures with good homogeneity.     

A calculation of the spin-orbit splitting of the X 2Π state of NO

Using Brion, Moser and Yamazaki's SCF LCAO MO the spin orbit splitting of the X ² state of NO has been calculated using various potentials. Experimentally W (² _3/2) –W (² _1/2) is known to be 122 cm^–1. Using an unscreened nuclear field we find a value of 328 cm^–1. Inclusion of screening due to electronic repulsions reduces this value to 283 cm^–1. Agreement with the experimental value may be obtained by reducing the orbital exponents in the 2 molecular orbital by 30% over the value given by Slater's rules.

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Zusammenfassung Die Spin-Bahn-Aufspaltung des X ² -Zustandes von NO wurde mit verschiedenen Potentialen unter Verwendung der SCF LCAO MOs von Brion, Moser und Yamazaki berechnet. Der experimentelle Wert für W (² _3/2) –W (² _1/2) beträgt 122 cm^–1. Die Rechnung mittels eines reinen Kernfeldes liefert den Wert 328 cm^–1 und unter Einschluß der Abschirmung durch die Elektronen 283 cm^–1. Übereinstimmung mit dem experimentellen Wert läßt sich erzielen, wenn man den Exponenten des 2-Zustandes 30% kleiner als nach den Slater Regeln macht.

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Résumé Avec les orbitals moléculaires SCF LCAO de Brion, Moses et Yamazaki, nous avons calculé le dédoublement spin-orbitale de l'état X ² de NO. La valeur expérimentale W (² _3/2) –W (² _1/2) est 122 cm^–1. Dans un champ nucléaire «sans écran» on trouve 328 cm^–1. L'inclu-sion de l'effet d'écran dû aux répulsions interélectroniques réduit cette valeur à 283 cm^–1. La valeur expérimentale s'obtient, si l'on réduit de 30% les exposants d'après Slater dans l'orbi-tale moléculaire 2.