Reaction of hot H atoms with CD3Br

Energetic H atoms produced by photolysis of gaseous HI react with CD₃Br by D abstraction (1) and Br abstraction (2) and possibly also by the substitution reactions (4) and (5). Yields of HD and CD₃H have been determined for several defined initial translational energies of H^*. The phenomenological threshold energy of reaction (1) is 53 ± 5 kJ/mol. Over the range of initial energies of 76–109 kJ mol the integral probability of reaction (1) increases substantially, but the sum of the integral probabilities of reactions (2) and (5) shows little change. The ratio of the sum of the integral yields of reactions (2) and (5) to the integral yield of reaction (1), when normalized to equal numbers of Br and D atoms, is 69 ± 33 at an initial energy of 76 kJ/mol and 31 ± 6 at 109 kJ/mol.     

Reaction of energetic hydrogen atoms with 1-chloropropane

The reaction of photochemically generated energetic hydrogen atoms with 1-chloropropane, reaction (1), has been examined for translational energies of H* in the range 40 to 110 kJ mol^?1. Integral probabilities for reaction (1) have been determined, and the phenomenological threshold energy is 47 ± 10 kJ mol^?1. The moderating effect of CO₂ on reaction (1) for hydrogen atoms of initial energy 108 kJ mol^?1 has also been studied. © 1993 John Wiley & Sons, Inc.     

Correlation of activation energies of radical–molecule metathesis reactions with enthalpic,polar, and steric parameters

It is shown that the activation energies E oF chlorine atom abstraction by cyclohexyl radicals and hydrogen atom abstraction by Cl atoms from polychloroalkanes can be correlated with the bond dissociation energies D and the Taft polar and steric substituent constants σ* and E_s by the expression: where ΔE and ΔD represent the differences between the E and D values of a given substrate and those of a reference compound (CH₃ substituted substrate) and α, ρ, and δ are the corresponding correlation coefficients. The use of this expression allows quantitative evaluation of the relative contribution of the various factors affecting the activation energies of these reactions and estimation of related thermochemical data.     

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.     

Kinetic Parameters for Direct Atomic Substitution Reactions

Experimental data (the rate constants and activation energies) for seven reactions of direct substitution of one atom for another D + CH₃R CH₂DR + H, D + NH₃ DNH₂ + H, D + H₂O HOD + H, F + CH₃X CH₃F + X (X = F, Cl, Br, and I) involving atoms D and F and molecules C₂H₆, H₂O, NH₃, CH₃F, CH₃Cl, CH₃Br, and CH₃I are analyzed using the parabolic model of a bimolecular radical reaction. The activation energies for the thermally neutral analogs of these substitution reactions are calculated. Atomic substitution involving deuterium atoms has a lower activation energy of a thermally neutral reaction than radical abstraction or substitution.     

Pd(Cu)在MgO(100)表面吸附CO和O2的理论研究

采用固体镶嵌势能模型和DFT/B3LYP方法研究了在Pd/MgO和Cu/MgO表面吸附CO和O₂分子的电子性质. 计算结果表明, 在完美MgO(100)表面Pd原子对CO和O₂的吸附能分别为206.5和84.8 kJ/mol, 因此可知Pd原子更容易吸附CO分子; 而当Pd原子附着于有氧缺陷的MgO表面时, 它对两种分子的吸附都非常弱. 相反, 附着于MgO表面的Cu原子对O₂分子的吸附更为有利, 其吸附能在140～155 kJ/mol之间. 研究结果还表明, 对于双分子吸附体系, 即CO＋CO, CO＋O₂, O₂＋O₂体系, 双分子之间的结合力可减小完美MgO表面上Pd原子与被吸附分子的相互作用, 使吸附能减少了46～96 kJ/mol. 而对于在MgO表面上的Cu原子, 只有O₂＋O₂ 体系使吸附能减少了大约50～71 kJ/mol.     

Theoretical investigation on identical anionic halide‐exchange SN2 reaction processes on N‐haloammonium cation NH3X+ (X = F,Cl, Br,and I)

CCSD(T) calculations have been used for identically nucleophilic substitution reactions on N‐haloammonium cation, X^? + NH₃X⁺ (X = F, Cl, Br, and I), with comparison of classic anionic S_N2 reactions, X^? + CH₃X. The described S_N2 reactions are characterized to a double curve potential, and separated charged reactants proceed to form transition state through a stronger complexation and a charge neutralization process. For title reactions X^? + NH₃X⁺, charge distributions, geometries, energy barriers, and their correlations have been investigated. Central barriers ΔE for X^? + NH₃X⁺ are found to be lower and lie within a relatively narrow range, decreasing in the following order: Cl (21.1 kJ/mol) > F (19.7 kJ/mol) > Br (10.9 kJ/mol) > I (9.1 kJ/mol). The overall barriers ΔE relative to the reactants are negative for all halogens: ?626.0 kJ/mol (F), ?494.1 kJ/mol (Cl), ?484.9 kJ/mol (Br), and ?458.5 kJ/mol (I). Stability energies of the ion–ion complexes ΔE_comp decrease in the order F (645.6 kJ/mol) > Cl (515.2 kJ/mol) > Br (495.8 kJ/mol) > I (467.6 kJ/mol), and are found to correlate well with halogen Mulliken electronegativities (R² = 0.972) and proton affinity of halogen anions X^? (R² = 0.996). Based on polarizable continuum model, solvent effects have investigated, which indicates solvents, especially polar and protic solvents lower the complexation energy dramatically, due to dually solvated reactant ions, and even character of double well potential in reactions X^? + CH₃X has disappeared. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical study of hydrogen bonded complexes of dimethyl disulfide or dimethyl peroxide with nitric acid

Ab initio and DFT calculations performed on the title systems revealed two types of structures for both DMDS-HNO₃ and DMDO-HNO₃ complexes. In both structures two hydrogen bonds are formed between the OH group interacting with one of sulfur (or oxygen) atoms and methyl CH group being a proton donor to one of the oxygen atoms of the NO₂ group of nitric acid. Depending on the location of the interacting methyl group with respect to the S or O acceptor of the main O-H?S(O) bond, the seven or eight-membered ring structures are formed. For all the structures, the most pronounced changes in geometric parameters upon interaction are observed for the proton donor molecule. The calculated binding energies are between −20.86 and −29.95 kJ/mol at MP2 and between −17.52 and −27.47 kJ/mol at B3LYP using the 6-311++G(2d,2p) basis set. The complexes involving disulfide are slightly weaker by ca. 6.7-8.6 kJ/mol than the corresponding peroxide complexes. The performed NBO analysis reveals that the charge transferred to σ*(OH) orbital of the nitric acid molecule comes mainly from the high p-character lone pair orbital of sulfur or oxygen atom being the hydrogen bond acceptor site in the disulfide or peroxide molecule.     

Vibrattonal excitation of molecules by collisions with “hot” hydrogen atoms from laser photolysis

Excimer laser (ArF) photolysis of diatomic and triatomic hydrides produces hydrogen atoms with translational energies in excess of 15000 cm^?1 per atom. Subsequent collisions of these “hot” atoms with CO₂ and N₂O produces vibrationally excited molecules which can be detected by their characteristic infrared emission.     

Kinetics of the gas-phase reaction between iodine and trifluorosilane and the bond dissociation energy D(F3Si?H)

The title reaction has been investigated in the temperature range 667–715K. The only reaction products were trifluorosilyl iodide and hydrogen iodide. The rate law was obeyed over a wide range of iodine and trifluorosilane pressures. This expression is consistent with an iodine atom abstraction mechanism and for the step log k₁(dm³/mol·sec) = (11.54 ± 0.17) ? (130.5 ± 2.2 kJ/mol)/RT In 10 has been deduced. From this the bond dissociation energy D(F₃Si? H) = (419 ± 5) kJ/mol (100.1 kcal/mol) is obtained. The kinetic andthermochemical implications of this value are discussed.     

Reactivity of the Ge–H,Sn–H,P–H,and Se–H Bonds in Radical Abstraction Reactions

The experimental data for the liquid- and gas-phase reactions of atoms and radicals with organoelement compounds R _{n – 1}E–H

Unimolecular Rate Constants for the HF and HCl Elimination Reactions from Chemically Activated CF2ClSH

Chemically activated CF₃SH, CFCl₂SH, and CF₂ClSH were formed through combination of SH and CF₃, CFCl₂, and CF₂Cl radicals, respectively. The SH radical was prepared by abstraction of an H‐atom from H₂S by the halocarbon radical produced during photolysis of (CF₃)₂C=O, (CFCl₂)₂C=O, or (CF₂Cl)₂C=O. 1,2‐HX (X = F, Cl) elimination reactions were observed from CF₃SH, CFCl₂SH, and CF₂ClSH with products detected by GC‐MS. The combination reaction of CF₂Cl radicals with SH radicals prepared CF₂ClSH molecules with approximately 318 kJ/mol of internal energy. The experimental rate constants for elimination of HCl and HF from CF₂ClSH were 3 ± 3 × 10¹⁰ and 2 ± 1 × 10⁹ s^?1, respectively. Comparison to Rice–Ramsperger–Kassel–Marcus (RRKM) calculated rate constants assigned the threshold energies as 171 ± 12 and 205 ± 12 kJ/mol for the unimolecular elimination of HCl and HF, respectively. Theoretical calculations using the B3PW91, MP2, and M062X methods with the 6311+G(2d,p) and 6‐31G(d',p') basis sets established that for a specific method the threshold energies differ by only 4 kJ/mol between the two different basis sets. There was wide variation among the three methods, but the M062X approach appeared to give threshold energies closest to the experimental values. Chemically activated CF₃SH and CFCl₂SH were also prepared with about 318 kcal mol^?1 of internal energy, and the HX (X = F, Cl) elimination reactions were observed. Only HCl loss was detected from CFCl₂SH, but the rate was too fast to measure with our kinetic method; however, based on our detection limit the HF elimination channel is at least 50 times slower.     

Massenspektrometrische Untersuchungen einfacher und gemischter Phosphortrihalogenide

Zusammenfassung Die Massenspektren von Gemischen aus PCl₃, PBr₃ und PJ₃ zeigen die Molekülionen aller durch Halogenaustausch möglichen Phosphortrihalogenide. Auftrittspotentialmessungen lieferten die Bildungsenthalpien H _B (PCl₂Br) _g =–274±10kJ/mol und H _B (PClBr₂) _g =–212±10kJ/mol. Die Ionisierungsenergien der Phosphortrihalogenide, die Cl, Br, J enthalten, stehen in enger Beziehung zur durchschnittlichen Elektronegativität der Halogenatome. Wie stoßinduzierte Zerfälle ergaben, ist in den Phosphorhalogenidionen die P–Br-Bindung schwächer als die P–Cl-Bindung.

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Mass spectrometric investigations of phosphorus trihalides and mixed phosphorus trihalides

The mass spectra of mixtures of PCl₃, PBr₃, and PI₃ contain molecular ions of all phosphorus trihalides, which are possible by halogen exchange. Appearance potential measurements gave the heats of formation H _B (PCl₂Br) _g =–274±10kJ/mol and H _B (PClBr₂) _g =–212±10kJ/mol. The ionization energies of Cl, Br, I containing phosphorus trihalides are closely related to the average electronegativity of the halogen atoms. Collision induced fragmentations showed for ions, that P–Br bonding is weaker than P–Cl bonding.

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Teil der DissertationK. Varmuza, Massenspektrometrische Untersuchungen an einigen Phosphortrihalogeniden, Techn. Hochschule Wien, 1970.     

Measuring the rate constant of the reaction between chlorine atoms and CHF<Subscript>2</Subscript>Br by Cl atom resonance fluorescence

The rate constant of the reaction between Cl atoms and CHF₂Br has been measured by chlorine atom resonance fluorescence in a flow reactor at temperatures of 295–368 K and a pressure of ~1.5 Torr. Lining the inner surface of the reactor with F-32L fluoroplastic makes the rate of the heterogeneous loss of chlorine atoms very low (k_het ≤ 5 s^–1). The rate constant of the reaction is given by the formula k = (4.23 ± 0.13) × 10^–12e^{(–15.56 ± 1.58)/RT} cm³ molecule^–1 s^–1 (with the activation energy in kJ/mol units). The possible role of this reaction in the extinguishing of fires producing high concentrations of chlorine atoms is discussed.     

The standard enthalpy of formation of fullerene chloride C<Subscript>60</Subscript>Cl<Subscript>30</Subscript>

A rotating-bomb calorimeter was used to measure the energy of combustion of crystalline fullerene chloride C₆₀Cl₃₀ · 0.09Cl₂, Δ_c U° = (?24474 ± 135 kJ/mol). The result was used to calculate the standard enthalpy of formation, Δ_f H° (C₆₀Cl₃₀, cr) = 135 ± 135 kJ/mol, and the C-Cl bond energy, 195 ± 5 kJ/mol. The C-X (X = F, F, Cl, and Br) bond energies in fullerene C₆₀ derivatives and other organic compounds are compared.     

Synthesis,complexing properties and molecular modelling of open chain receptors of barbiturates derived from 2,6-diamino pyridine

Three new derivatives of 2,6-diacyldiaminopyridine are reported. NMR shift titrations were performed in CDCl₃ with barbiturates. The diamide1 affords a greater complexation energy (–13.00 kJ mol^–1) with bemegride than the dithioamide2 (–9.15 kJ mol^–1). This result, unexpected on the basis of the proton acidities, is explained by the great torsion energy induced in2 by the bulky sulfur atom. Compounds3 and4 present unusual four and five H-bond features with barbital and relatively weak complexation energies (–9.53 and –16.34 kJ mol^–1, respectively). Molecular mechanics indicates that ligand4 displays a helical secondary structure which is disrupted by complexation. Calculations of the H-bond energies (E _calc.) of the intermolecular assemblies with barbital or phenobarbital and other host-guest complexes given in the literature give a good correlation (r=0.98) with experimental values: E _calc.=1.07 G _a–42.0. Limitations of this relation are discussed.     

Rate constants of reactions of chlorine atoms with aliphatic hydrocarbons and halogen derivatives in the liquid phase

The kinetics of liquid phase chlorination of methane in a difluorodichloromethane medium has been studied in a temperature interval of 293–150 K. The value of activation energy found for the hydrogen abstraction stage by a chlorine atom (E₁) equals 14.2 ± 2.5 kJ/mol, with the processes of chlorine atoms recombination and the cage effect being taken into account. The method of competitive reactions has been employed to assess the constants of reaction of chlorine atoms (k₁) with ethane, propane, hexane, ethylene, allyl bromide, allyl chloride, ethyl chloride, and cyclohexane in nonpolar solvents, viz. difluorodichloromethane and 1,2-dibromotetrafluoroethane. The values (k₁) obtained in the liquid phaseare two to four orders lower than those in the gas phase, while the activation energy is 2–6 kJ/mol higher.     

The π-hole tetrel bond between X2TO and CO2: Substituent effects and its potential adsorptivity for CO2

Quantum chemical calculations are applied to study the complexes between X₂TO (X = H, F, Cl, Br, CH₃; T = C, Si, Ge, Sn) and CO₂. The carbon atom of CO₂ as a Lewis acid participates in the C···O carbon bond, whereas its oxygen atom as a base engages in the O···T tetrel bond with X₂TO. Most of complexes are stabilized by a combination of both C···O and O···T interactions. The interaction energy increases in the T = C < Ge < Sn < Si sequence for most complexes. Both the electron-withdrawing halogen group and the electron-donating methyl group increase the interaction energy, up to 51 kJ/mol in F₂SiO···CO₂. One F₂SiO molecule can bind with different numbers of CO₂ molecules (1–4); as the number of CO₂ molecules increases, the average interaction energy for each CO₂ decreases and each CO₂ molecule can contribute with at least 27 kJ/mol. Therefore, silicon-containing molecules are good absorbents for CO₂.     

A fully ab initio potential energy surface for ClH2 reactive system

Anab initio analytical potential energy surface called BW3 for the ClH₂ reactive system is presented. The fit of this surface is based on about 1 200ab initio energy points, computed with multi-reference configuration interaction(MRCI) and scaling external correlation (SEC) method and a very large basis set. The precision in the fit is very high. The BW3 surface could reproduce correctly the dissociation energy of H₂ and HCl, and the endothermicity of the Cl + H₂ abstraction reaction. For the Cl + H₂ abstraction reaction, the saddle point of BW3 lies in collinear geometries, and the barrier height is 32.84 kJ/mol; for the H + ClH exchange reaction, the barrier of BW3 is also linear, with a height of 77.40 kJ/mol.