scholarly journals Predicting activation energies for vacancy-mediated diffusion in alloys using a transition-state cluster expansion

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Chenyang Li ◽  
Thomas Nilson ◽  
Liang Cao ◽  
Tim Mueller
Keyword(s):  
Transition State ◽  
Cluster Expansion ◽  
Activation Energies ◽  
Diffusion In Alloys

scholarly journals An aniline dication-like transition state in the Bamberger rearrangement

2013 ◽  
Vol 9 ◽  
pp. 1073-1082 ◽  
Author(s):  
Shinichi Yamabe ◽  
Guixiang Zeng ◽  
Wei Guan ◽  
Shigeyoshi Sakaki
Keyword(s):  
Activation Energy ◽  
Dft Calculations ◽  
Transition State ◽  
Water Cluster ◽  
Transition States ◽  
Activation Energies ◽  
Nitrenium Ion ◽  
Proton Transfers ◽  
First Time

A Bamberger rearrangement of N-phenylhydroxylamine, Ph–N(OH)H, to p-aminophenol was investigated by DFT calculations for the first time. The nitrenium ion, C6H5–NH+, suggested and seemingly established as an intermediate was calculated to be absent owing to the high nucleophilicity of the water cluster around it. First, a reaction of the monoprotonated system, Ph–N(OH)H + H3O+(H2O) n (n = 4 and 14) was examined. However, the rate-determining transition states involving proton transfers were calculated to have much larger activation energies than the experimental one. Second, a reaction of the diprotonated system, Ph–N(OH)H + (H3O+)2(H2O)13, was traced. An activation energy similar to the experimental one was obtained. A new mechanism of the rearrangement including the aniline dication-like transition state was proposed.

Theoretical Studies for Ozonide Formation During the Ozonolysis of Bicyclic Endoperoxides

2013 ◽  
Vol 66 (8) ◽  
pp. 891 ◽  
Author(s):  
Nicole M. Cain ◽  
Josh L. Hixson ◽  
Dennis K. Taylor
Keyword(s):  
Transition State ◽  
Electron Correlation ◽  
Transition States ◽  
Activation Energies ◽  
Basis Set ◽  
Theoretical Studies ◽  
Theoretical Investigations ◽  
Central Oxygen

Theoretical investigations on the treatment of bicyclic endoperoxides (1,2-dioxines) with ozone at the HF/6–31G*, MP2/6–31G* or 6–311G*, and DFT(B3LYP)/6–31G* levels of theory indicate that the estimated activation energies for formation of the possible endo-endo, endo-exo, exo-endo, or exo-exo transition states along with the formation of the primary ozonides and product ozonides are very sensitive to effects of electron correlation and basis set. This study suggests that MP2/6–311G* is the best level of theory for evaluating such systems. At the MP2/6–311G* level of theory it was found that the transition state for primary ozonide formation was lowest in energy when ozone approaches in an endo facial fashion with a further 3 kJ mol–1 stabilisation seen when the central oxygen within the primary ozonide protrudes outwards (exo) as opposed to inwards (endo). The product ozonides are predicted to be more stable than the combined starting materials by some 380–580 kJ mol–1 depending on the level of theory, clearly highlighting the substantive exothermic nature of this type of ozonolysis reaction.

Synthesis of azacyclic compounds by an aminium radical route: orbital overlap requirements

1976 ◽  
Vol 54 (15) ◽  
pp. 2385-2401 ◽  
Author(s):  
Richard A. Perry ◽  
Shi C. Chen ◽  
B. C. Menon ◽  
Kaoru Hanaya ◽  
Yuan L. Chow.
Keyword(s):  
Transition State ◽  
Excellent Agreement ◽  
Metal Ion ◽  
Early Stage ◽  
Hydrogen Abstraction ◽  
Activation Energies ◽  
Model Compounds ◽  
Steric Strain ◽  
Factors Associated ◽  
Lower Activation

Model compounds of Δ4,5-, Δ5,6-, and Δ6,7-alkenylnitrosamines were synthesized and photolyzed to generate the corresponding alkenylaminium radicals. The Δ5,6-alkenylaminium radicals underwent efficient intramolecular addition leading to the exclusive formation of pyrrolidine derivatives, the yield of which was lower if the steric strain and hindrance were severe in the cyclization transition state. The Δ6,7-alkenylaminium radical cyclized inefficiently to piperidine derivatives and the Δ4,5-alkenylaminium radicals did not appear to cyclize; in both cases other pathways having lower activation energies, such as elimination and hydrogen abstraction, predominated. Evidence that the direction of cyclization is controlled by the degree of p-orbital overlap, but not by stability of the developing products, in the transition state is presented. The stereochemical factors associated with the overlap determined the yields of the cyclization products. This is in excellent agreement with the fact that the transition state of cyclization is reached at an early stage in the reaction coordinate. Metal ion catalyzed or radical initiated decomposition of some alkenyl chloramines were found either to cyclize to a mixture of pyrrolidine and piperidine derivatives or to undergo no cyclization.

THE TRANSFER REACTIONS OF HALOGEN ATOMS

1960 ◽  
Vol 38 (10) ◽  
pp. 1643-1647 ◽  
Author(s):  
G. C. Fettis ◽  
J. H. Knox ◽  
A. F. Trotman-Dickenson
Keyword(s):  
Transition State ◽  
Transition State Theory ◽  
Hydrogen Bromide ◽  
Bromine Atom ◽  
Activation Energies ◽  
State Theory ◽  
Transfer Reactions ◽  
Methyl Halides ◽  
Alkyl Radicals ◽  
Bond Strengths

Extensive results on the reactions of fluorine, chlorine, and bromine atoms with alkanes and with some other molecules have been obtained from the study of competitive halogenations. The comparison of the A factors of the reactions provides an excellent test of the transition state theory. The activation energies of the bromine atom reactions can be combined with measurements of the activation energies for the reactions of alkyl radicals with hydrogen bromide to yield unusually reliable values of bond strengths. Information on the influence of polar effects on the activation energies of atomic reactions can be obtained from results on the reactions of fluorine and chlorine atoms with methyl halides.

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