Non-steady-state kinetic study of the SN2 reaction between p-nitrophenoxide ion and methyl iodide in acetonitrile

Analysis of non-steady-state kinetic data for the title reaction with tetrabutylammonium counter ions in acetonitrile in the presence and absence of sodium ions rules out the ion-pair dissociation mechanism. The reinterpretation of our data by Humeres and Bentley (Org. Biomol. Chem., 2003, 1, 1969-1971) was based on a series of assumptions that are shown to be invalid by kinetic experiments.     

A kinetic study of the gas phase reaction between trimethylsilane and methyl chloride

The kinetics of the gas phase reaction between trimethylsilane and methyl chloride have been investigated between 429 and 494° in packed and unpacked quartz vessels. Methane and trimethylchlorosidane are the only products formed in substantial quantity, and the results are consistent with their bcing produced in a radical chain reaction propagated in the gas phase with heterogeneous initiation and termination. It is suggested that in the packed vessel initiation is by dissociative desorption of trimethylsilane from singly-occupied surface sites, but in the unpacked vessel a more complex initiation mechanism appears to operate, and it is tentatively suggested that methyl chloride is dissociatively adsorbed, the chlorine atom then reacts with adsorbed trimethylsilane at the surface, and a dimethylchiorosilane molecule and a methyl radical are finally desorbed into the gas phase.     

Substituent effects on SN2 reaction between substituted benzyl chloride and chloride ion in gas phase

Nucleophilic substitution reaction between some substituted benzyl chlorides and chloride ion has been investigated by ab initio and DFT methods. New calculated energy data are in better agreement with experimental data. The electron‐withdrawing groups increase the energy barriers and the electron‐donating groups decrease them. The changes of geometrical parameters and energy data are in good agreement with the results of atoms in molecules and natural bond orbital analyses. The relationship between Hammett coefficients and energy data (and geometry parameters) has been established and the ρ constant has been calculated for this reaction. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

SN2 reactions in the gas phase. Nucleophilicity effects

The heats and entropies of gas phase association of chloride, bromide and iodide with the respective methyl halides are reported. Comparison of these results with results published for S_N2 reactions in solution suggests that the solvent is the dominant factor in determining relative halide nucleophilicities for the reactions in solution.     

Ab initio MO study of the solvent effect on the SN2 reaction of the trimethylsulfonium cation with chloride anion

A recently developed ab initio MO theory including solvent effects has been applied to a typical cation-anion reaction, the S_N2 reaction of the trimethylsulfonium cation with the chloride anion. In the gas phase, the trimethylsulfonium and chloride ions are unstabilized, and the reaction is expected to proceed rapidly. In aqueous solution, the reactant ions are largely stabilized, and the reaction has been predicted to be endothermic, with an activation energy of 30–40 kcal/mol. This potential energy profile, which agrees with experimental results, has been well elucidated by differential solvation at several stages of the reaction path. At the transition state of this reaction, the C and H atoms in the transferring CH₃ group are almost in a plane that is perpendicular to the Cl(SINGLE BOND)C(SINGLE BOND)S line, reflecting the concerted nature of the reaction. The population analysis has shown that the electrons in the C(SINGLE BOND)S bond are mostly withdrawn by the sulfur atom at the transition state and that the electron transfer from Cl to CH₃ occurs after the transition state. The calculated activation energy for the reaction in ethanol is smaller than that in water. This agrees with experiments. © 1996 John Wiley & Sons, Inc.     

Non-steady-state kinetic study of the SN2 reaction between p-nitrophenoxide ion and methyl iodide in aprotic solvents containing water. Evidence for a 2-step mechanism

Non-steady-state kinetic studies reveal that the SN2 reaction between p-nitrophenoxide ion and methyl iodide in acetonitrile containing water follows a 2-step mechanism involving the formation of a kinetically significant intermediate.     

SN2 reactions in the gas phase. Alkyl group structural effects

The gas phase heats and entropies of S_N2-like association of bromide ions with a series of alkyl bromides are reported. Comparison of this data with published data for the same reactions in solution suggests that the alkyl group structural effects on S_N2 reactivity in solution are controlled entirely by the solvent.     

SN2 reactions in the gas phase. Structure of the transition state

The alkylhalide-halide association ions, [RX₂]^? that are observed in the negative chemical ionization mass spectra of alkyl halides appear to be directly related to the corresponding S_N2 transition states in solution. ‘Frontside’ association of halide ions with bridgehead alkyl halides does not occur in our system. The Change in heats and entropies of association for the chloromethane series is consistent with delocalization in the [RX]₂^? ions.     

A computational study of the effect of bending on secondary kinetic isotope effects in SN2 transition states

Using conventional transition state theory, the secondary deuterium kinetic isotope effect (KIE) in the inversion SN2 reaction of CH3F and F- is calculated to be small, 0.98 (T = 298 K). This is shown to be the result of a balance among opposing entropy and enthalpy terms. By contrast, KIE in the retention SN2 mechanism is calculated to be large (1.5). Accordingly, KIE is a potential observable for discriminating between the two mechanisms. Large KIE's are also found for the inversion and retention mechanisms of the ion pair reactions between CH3F and LiF. All of the transition structures leading to large KIE's have a bent FCF angle and an imaginary frequency that is sensitive to deuterium labeling.     

The gas phase reaction between CO2 and lanthanide atoms. A test of a model for the isokinetic effect

Summary Co₃O₄, NiCo₂O₄ and LaCo₂O₄catalysts were synthesizedby the citric acid-ligated method. These catalysts containing Co-oxide active components can largely lower the temperature of soot combustion under tight contact conditions. Under the conditions of loose contact NiCo₂O₄ cannot promote soot combustion, but LaCo₂O₄ can effectively promote soot combustion because the nanometric perovskite-type catalyst LaCoO₃produced in the LaCo₂O₄sample.</o:p>     

Ion-Molecule reaction in the gas phase part VI Regioselective SN2 reaction from terpenoid diastereoisomeric diols using CI/NH

A stereospecific and regioselective S_N2 mechanism (Walden inversion) is observed during studies involving modified terpenoid epimeric diols in a high-pressure ion source using ammonia as a reagent gas.     

Steric retardation of SN2 reactions in the gas phase and solution

The gas-phase S(N)2 reactions of chloride with ethyl and neopentyl chlorides and their alpha-cyano derivatives have been explored with B3LYP, CBS-QB3, and PDDG/PM3 calculations. Calculations predict that the steric effect of the tert-butyl group raises the activation energy by about 6 kcal/mol relative to methyl in both cases. Solvent effects have been computed with QM/MM Monte Carlo simulations for DMSO, methanol, and water, as well as with a polarizable continuum model, CPCM. Solvents cause a large increase in the activation energies of these reactions but have a very small differential effect on the ethyl and neopentyl substrates and their cyano derivatives. The theoretical results contrast with previous conclusions that were based upon gas-phase rate measurements.     

DFT study and Monte Carlo simulation on proton transfers of 2-amino-2-oxazoline, 2-amino-2-thiazoline, and 2-amino-2-imidazoline in the gas phase and in water

Density functional theory (DFT) and Monte Carlo (MC) simulation with free energy perturbation (FEP) techniques have been used to study the tautomeric proton transfer reaction of 2-amino-2-oxazoline, 2-amino-2-thiazoline, and 2-amino-2-imidazoline in the gas phase and in water. Two reaction pathways were considered: the direct and water-assisted transfers. The optimized structures and thermodynamic properties of stationary points for the title reaction system in the gas phase were calculated at the B3LYP/6-311+G(d, p) level of theory. The potential energy profiles along the minimum energy path in the gas phase and in water were obtained. The study of the solvent effect of water on the proton transfer of 2-amino-2-oxozoline, 2-amino-2-thiazoline, and 2-amino-2-imidazoline indicates that water as a solvent is favorable for the water-assisted process and slows down the rate of the direct transfer pathway.     

Quantum chemical study of pentafluorophenylxenonium pentafluorobenzoate in the gas phase and acetonitrile solution

Russian Journal of General Chemistry -     

Theoretical studies on the reaction of pentafulvenone with water in gas phase and aqueous solvent

In gas phase, the hydrations of pentafulvenone to generate three types of cyclopentadienyl carboxylic acids are studied theoretically at the MP2/6-311+G**//B3LYP/6-311+G** level. A water molecule attacking the C=O double bond of pentafulvenone can yield cyclopentadienyl carboxylic acids via the formation of fulvenediols, and attacking the C=C double bond of pentafulvenone can directly yield cyclopentadienyl carboxylic acid. The barriers of rate-determining transition states are 42.2 and 30.4 kcal mol⁻¹, respectively. The barriers of rate-determining transition states for two water molecules system are 20.2 and 19.6 kcal mol⁻¹, respectively. The products can isomerize to each other. In aqueous solvent, the hydrations of pentafulvenone are investigated using PCM-UAHF model at the MP2 (PCM)/6-311+G**// B3LYP (PCM)/6-311+G** and MP2 (PCM)/6-311+G**// B3LYP/6-311+G** levels. The barriers of all rate-determining transition states are decreased. The added water molecule acts as catalyst in both gas phase and aqueous solvent. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A computational study on the gas phase reaction of Os^＋ with N2O

The reaction of Os~+(~6D,~4F) with N_2O has been investigated at B3LYP/TZVP and CCSD(T)/6-311+G~* levels of theory.The mechanisms corresponding to O-atom and N-atom transfer reactions have been revealed.It was found that on the sextet reaction surface both the O-atom and N-atom transfer reactions undergo through direct-abstraction mechanism,leading to the formation of OsO~+ and OsN~+,whereas on quartet surface the two reactions undergo through O-N bond or N-N bond insertion mechanism.The calculated energ...     

A kinetic study of the reaction between formic acid and HoBr

The reaction between formic acid and HOBr in strongly acid aqueous media was studied by absorption spectrophotometry at 298 K. Bromine, the monitored species, displays a transient behavior, gradually rising up to a maximum and then decaying with first-order kinetics. Reaction rates, expressed as R = -dC_Br2/dt, depend on the concentrations of HCOOH (0.1–1.4M), HOBr (0.3–1.5 × 10^?3 M), and H⁺ (0.1–1.0M). The mechanism with k₁ =1.04 ± 0.20M^?1· s_?1, k₃ = 20.2M^?1, quantitatively accounts for all observations within experimental error.     

A theoretical study on the mechanism and thermodynamics of ozone-water gas phase reaction

Ozone water reaction including a complex was studied at the MP2/6-311++G(d,p) and CCSD/6-311++G(2df,2p)//MP2/6-311++G(d,p) levels of theory. The interaction between water oxygen and central oxygen of ozone produces stable H₂O-O₃ complex with no barrier. With decomposition of this complex through H-abstraction by O₃ and O-abstraction by H₂O, three possible product channels were found. Intrinsic reaction coordinate, topological analyses of atom in molecule, and vibrational frequency calculation have been used to confirm the preferred mechanism. Thermodynamic data at T = 298.15 K and atmospheric pressure have been calculated. The results show that the production of hydrogen peroxide is the main reaction channel with ΔG = ?21.112 kJ mol^-1.     

A two‐state reactivity rationale for the reaction of ta atom with acetonitrile in the gas phase

The spin‐forbidden reaction mechanism of Ta (⁴F, 5d³6s²) with CH₃CN, on two different potential surfaces (PESs) has been investigated at the B3LYP, MP2, and CCSD level of theory. Crossing points between the PESs are located using different methods, and possible spin inversion processes are discussed by means of spin‐orbit coupling calculations. As a result, the reaction system will change its spin multiplicities near this crossing seam, leading to a significant decrease in the barrier of ^2‐4TS3 from 24.17 to 5.36 kcal/mol, which makes the reaction access to a lower energy pathway and accelerate the reaction rate. © 2012 Wiley Periodicals, Inc.     

Theoretical study on the reaction mechanism of VO2+ with propyne in gas phase

Possible molecular mechanisms of the gas-phase ion/molecule reaction of VO2+ in its lowest singlet and triplet states (1A1/3A' ') with propyne have been investigated theoretically by density functional theory (DFT) methods. The geometries, energetic values, and bonding features of all stationary and intersystem crossing points involved in the five different reaction pathways (paths 1-5), in both high-spin (triplet) and low-spin (singlet) surfaces, are reported and analyzed. The oxidation reaction starts by a hydrogen transfer from propyne molecule to the vanadyl complex, followed by oxygen migration to the hydrocarbon moiety. A hydride transfer process to the vanadium atom opens four different reaction courses, paths 1-4, while path 5 arises from a hydrogen transfer process to the hydroxyl group. Five crossing points between high- and low-spin states are found: one of them takes place before the first branching point, while the others occur along path 1. Four different exit channels are found: elimination of hydrogen molecule to yield propynaldehyde and VO+ (1Sigma/3Sigma); formation of propynaldehyde and the moiety V-(OH2)+; and two elimination processes of water molecule to yield cationic products, Prod-fc+ and Prod-dc+ where the vanadium atom adopts a four- and di-coordinate structure, respectively.