SN2 reactions in the gas phase. Transition states for the reaction: Cl− + RBr = ClR + Br−, where R = CH3, C2H5, and iso-C3H7, from abinitio calculations and comparison with experiment. Solvent effects

1989 ◽  
Vol 67 (8) ◽  
pp. 1262-1267 ◽  
Author(s):  
Kimihiko Hirao ◽  
Paul Kebarle
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Aqueous Solution ◽  
Transition State ◽  
Gas Phase ◽  
Closed Shell ◽  
Basis Set ◽  
Phase Reaction ◽  
Ion Molecule Reactions ◽  
Abinitio Calculations

The geometries and the energies of the reactants, transition state, and products for the gas phase reaction: Cl− + CH3Br = ClCH3 + Br−, were obtained from abinitio calculations using a closed shell SCF method with a MINI basis set developed by Huzinaga etal. The energy changes predicted by the calculations are found in good agreement with the experimental data. The energies and geometries of the reactants and the transition state for the gas phase reactions: Cl− + RBr = ClR + Br−, where R = C2H5 and iso-C3H7, were also obtained. The resulting activation energies follow the same trend as the experimental data: Me < Et < iso-Pr; however, the predicted increase of activation energy is considerably larger. The energies and geometries for the reactants, transition state, and products of the gas phase ion-dihydrate reaction: Cl−(H2O)2 + CH3Br → H2O(ClCH3Br)−H2O → Br−(H2O)2 + CH3Cl were obtained as well. These data provide an interesting comparison with experimental results in aqueous solution. The reaction coordinate of the ion-dihydrate reaction is very much closer to that for aqueous solution than to that for the gas phase. Keywords: nucleophilic substitution reactions, ion–molecule reactions, activation energy.

The thermal decompositions of carbamates. II. Methyl N-methylcarbamate

1972 ◽  
Vol 25 (7) ◽  
pp. 1453 ◽  
Author(s):  
NJ Daly ◽  
F Ziolkowski
Keyword(s):  
Activation Energy ◽  
Transition State ◽  
Gas Phase ◽  
Rate Constants ◽  
Volume Ratio ◽  
Reaction Vessel ◽  
Phase Reaction ◽  
Methyl Isocyanate ◽  
Gas Phase Reaction ◽  
First Order

Methyl N-methyloarbamate decomposes in the range 370-422� to give methyl isocyanate and methanol. The reaction is first order in carbamate, and the variation of the rate constants with temperature is given by the equation. k = 1012.39 exp(-4806O/RT) (s-l; activation energy in cal mol-l) Rate constants are unaffected by the addition of isobutene or by increase in the surface to volume ratio of the reaction vessel. The addition of alcohols or amines does not reverse the process. The decomposition is considered to be a homogeneous, unimolecular gas-phase reaction, probably proceeding through a four-centred transition state.

Gas-phase reaction of CeVO5+ cluster ions with C2H4: the reactivity of cluster bonded peroxides

2015 ◽  
Vol 44 (7) ◽  
pp. 3128-3135 ◽  
Author(s):  
Jia-Bi Ma ◽  
Jing-Heng Meng ◽  
Sheng-Gui He
Keyword(s):  
Electronic Structure ◽  
Gas Phase ◽  
Closed Shell ◽  
Cluster Ions ◽  
Phase Reaction ◽  
Gas Phase Reaction ◽  
Metal Oxide Clusters ◽  
Transition Metal Oxide Clusters ◽  
Hydrocarbon Molecules ◽  
First Time

The reactivity of the peroxide unit with hydrocarbon molecules on transition metal oxide clusters with a closed-shell electronic structure has been identified for the first time.

Thermodynamic control in the reactions of gas phase anions. An abinitio and ion cyclotron resonance study of the reactions of anions with diborane

1985 ◽  
Vol 63 (2) ◽  
pp. 281-287 ◽  
Author(s):  
O. Elsenstein ◽  
M. Kayser ◽  
M. Roy ◽  
T. B. McMahon
Keyword(s):  
Gas Phase ◽  
Cyclotron Resonance ◽  
Reaction Pathway ◽  
Basis Set ◽  
Resonance Spectroscopy ◽  
Ion Cyclotron Resonance ◽  
Ion Molecule Reactions ◽  
Ion Cyclotron ◽  
Reaction Channels ◽  
Gas Phase Ion

The gas phase ion molecule reactions of a number of anions, X−, with diborane, B2H6 have been investigated using ion cyclotron resonance spectroscopy. Two distinct reaction channels are observed in addition to simple proton transfer. The first of these is production of BH4− and BH2X while the second is formation of BH3X− and BH3. In order to determine the importance of thermodynamic factors in the course of reaction abinitio calculations have been carried out on the species involved to obtain the relative stabilities of the two possible pairs of products. The 4-31 +G basis set incorporating additional flat s and p functions has been used since this basis set has been demonstrated to give the most accurate description of anions to date. The results obtained indicate that the thermochemical factors are instrumental in determining the reaction pathway.

Structures, binding energies, and thermodynamic functions of NH4+, NH3•+, and their H2O complexes

1993 ◽  
Vol 71 (9) ◽  
pp. 1368-1377 ◽  
Author(s):  
David A. Armstrong ◽  
Arvi Rauk ◽  
Dake Yu
Keyword(s):  
Experimental Data ◽  
Gas Phase ◽  
Thermodynamic Functions ◽  
Hydration Shell ◽  
Binding Energies ◽  
Basis Set ◽  
Free Energies ◽  
Hydrated Complexes ◽  
Optimized Geometries ◽  
First Hydration Shell

Ab initio calculations are performed for [Formula: see text] and [Formula: see text] complexes for n = 0–5. For n = 0 and 1, the geometries of the complexes are optimized at the HF/6-31 + G* and MP2/6-31 + G* levels, and the energies are evaluated at the G2 level. For n = 2–5, the geometry optimizations and frequency calculations are carried out at the HF/6-31 + G* level, and the MP2/6-31 + G* energies are calculated at the HF optimized geometries. Basis set superposition errors are corrected by the Boys–Bernardi scheme at the HF/6-31 + G* level. The gas phase thermodynamic properties [Formula: see text] are evaluated as functions of temperature using standard statistical methods. Based on the calculated binding energies and the thermodynamic functions, the incremental changes in enthalpies and free energies, ΔHn and ΔGn, for the gas phase equilibria (H2O)n−1 M+ + H2O → (H2O)nM+ for M+ = NH4+ and NH3•+, are evaluated in comparison with the experimental data for [Formula: see text] the present results suggest conformations for the hydrated complexes observed in the experiments. The total free energy change for filling the first hydration shell is significantly more negative for NH3•+ than for NH4+.

scholarly journals Temperature and pH effects on the kinetics of 2-aminophenol auto-oxidation in aqueous solution

2003 ◽  
Vol 1 (3) ◽  
pp. 233-241 ◽  
Author(s):  
Dumitru Oancea ◽  
Mihaela Puiu
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Aqueous Solution ◽  
Ph Effects ◽  
Influence Of Temperature ◽  
First Order ◽  
Incremental Methods ◽  
First Order Kinetics ◽  
Ph Range ◽  
Kinetics Of

AbstractThe kinetics of the auto-oxidation of 2-aminophenol (OAP) to 2-amino-phenoxazin-3-one (APX) was followed in air-saturated aqueous solutions and the influence of temperature and pH on the auto-oxidation rate was studied. The kinetic analysis was based on a spectrophotometric method following the increase of the absorbance of APX. The process follows first order kinetics according to the rate law—d[OAP]/dt=k′[OAP]. The experimental data, within the pH range 4–9.85, were analyzed using both differential and incremental methods. The temperature variation of the overall rate constant was studied at pH=9.85 within the range 25–50°C and the corresponding activation energy was evaluated.

scholarly journals Diol Mediated Tautomerization of Glycine: a DFT Study

2019 ◽  
Vol 16 (1) ◽  
pp. 33-39
Author(s):  
Francis Suh ◽  
Vanessa Rivera ◽  
Ruben Parra
Keyword(s):  
Activation Energy ◽  
Aqueous Solution ◽  
Hydrogen Bonds ◽  
Proton Transfer ◽  
Gas Phase ◽  
Activation Energies ◽  
Dft Study ◽  
Hydroxyl Groups ◽  
Neutral Process ◽  
Product Forms

The tautomerization of glycine via a triple proton transfer was investigated both in the gas phase and in aqueous solution using the B3LYP/6-31+G(d,p) level of theory. Fully optimized complexes of the neutral and zwitterion forms of glycine with 1,3-propanediol were used for the reactant and product forms, respectively. The hydroxyl groups in the diol are conveniently oriented for glycine tautomerization through a concerted triple proton transfer facilitated by a network of three hydrogen bonds: N-H…O-H…O-H…O=C. The activation energy for the zwitterion à neutral process increases in solution. Also, the diol-glycine complex favors the neutral over the zwitterion form in a vacuum, but the opposite is true in solution. For comparative purposes, the tautomerization of glycine via a three-proton transfer mediated by two molecules of water was also examined. The results are qualitatively similar, albeit with activation energies that are smaller to those found in the corresponding diol-mediated tautomerization. KEYWORDS: Glycine; zwitterion, diol-mediated tautomerization; water-mediated tautomerization

scholarly journals Models of Hot Cores with Complex Molecules

2011 ◽  
Vol 7 (S280) ◽  
pp. 79-87
Author(s):  
Susanna L. Widicus Weaver ◽  
Robin T. Garrod ◽  
Jacob C. Laas ◽  
Eric Herbst
Keyword(s):  
Gas Phase ◽  
Reaction Pathways ◽  
High Mass ◽  
Phase Reaction ◽  
Complex Molecules ◽  
Warm Up ◽  
Ion Molecule Reactions ◽  
Relative Abundances ◽  
Surface Ice ◽  
Grain Surface

AbstractRecent models of hot cores have incorporated previously-uninvestigated chemical pathways that lead to the formation of complex organic molecules (COMs; i.e. species containing six or more atoms). In addition to the gas-phase ion-molecule reactions long thought to dominate the organic chemistry in these regions, these models now include photodissociation-driven grain surface reaction pathways that can also lead to COMs. Here, simple grain surface ice species photodissociate to form small radicals such as OH, CH3, CH2OH, CH3O, HCO, and NH2. These species become mobile at temperatures above 30 K during the warm-up phase of star formation. Radical-radical addition reactions on grain surfaces can then form an array of COMs that are ejected into the gas phase at higher temperatures. Photodissociation experiments on pure and mixed ices also show that these complex molecules can indeed form from simple species. The molecules predicted to form from this type of chemistry reasonably match the organic inventory observed in high mass hot cores such as Sgr B2(N) and Orion-KL. However, the relative abundances of the observed molecules differ from the predicted values, and also differ between sources. Given this disparity, it remains unclear whether grain surface chemistry governed by photodissociation is the dominant mechanism for the formation of COMs, or whether other unexplored gas-phase reaction pathways could also contribute significantly to their formation. The influence that the physical conditions of the source have on the chemical inventory also remains unclear. Here we overview the chemical pathways for COM formation in hot cores. We also present new modeling results that begin to narrow down the possible routes for production of COMs based on the observed relative abundances of methyl formate (HCOOCH3) and its C2H4O2 structural isomers.

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