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.

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.

The Silicon-Directed Tiffeneau - Demjanov Reaction: Some Theoretical Studies

2004 ◽  
Vol 57 (9) ◽  
pp. 869 ◽  
Author(s):  
Melanie McClure ◽  
Carl Schiesser ◽  
Jonathan White
Keyword(s):  
Transition State ◽  
Activation Barrier ◽  
Basis Set ◽  
Chain Extension ◽  
Theoretical Studies ◽  
Leaving Group ◽  
Group Water ◽  
Leaving Groups ◽  
Early Transition

The Tiffeneau–Demjanov chain extension reaction was modelled using the B3LYP/6-31G* basis set for both diazonium and water leaving groups. The chain extension of 12 with the diazonium leaving group occurs with an early transition state, a low activation barrier, and very little participation by the silicon substituent. Chain extension of 15, involving displacement of the less reactive leaving group water, occurs with a later transition state, a significantly higher activation barrier, and with greater participation by the silicon substituent.

scholarly journals Benchmarking the Fluxional Processes of Organometallic Piano-Stool Complexes

Molecules ◽  
2021 ◽  
Vol 26 (8) ◽  
pp. 2310
Author(s):  
Nathan C. Frey ◽  
Eric Van Dornshuld ◽  
Charles Edwin Webster
Keyword(s):  
Transition Metals ◽  
Density Functional ◽  
Chemical Shifts ◽  
Transition States ◽  
Electronic Energy ◽  
Basis Set ◽  
Composite Approach ◽  
Temperature Regimes ◽  
Correlation Consistent Composite Approach ◽  
Correlation Consistent

The correlation consistent Composite Approach for transition metals (ccCA-TM) and density functional theory (DFT) computations have been applied to investigate the fluxional mechanisms of cyclooctatetraene tricarbonyl chromium ((COT)Cr(CO)3) and 1,3,5,7-tetramethylcyclooctatetraene tricarbonyl chromium, molybdenum, and tungsten ((TMCOT)M(CO)3 (M = Cr, Mo, and W)) complexes. The geometries of (COT)Cr(CO)3 were fully characterized with the PBEPBE, PBE0, B3LYP, and B97-1 functionals with various basis set/ECP combinations, while all investigated (TMCOT)M(CO)3 complexes were fully characterized with the PBEPBE, PBE0, and B3LYP methods. The energetics of the fluxional dynamics of (COT)Cr(CO)3 were examined using the correlation consistent Composite Approach for transition metals (ccCA-TM) to provide reliable energy benchmarks for corresponding DFT results. The PBE0/BS1 results are in semiquantitative agreement with the ccCA-TM results. Various transition states were identified for the fluxional processes of (COT)Cr(CO)3. The PBEPBE/BS1 energetics indicate that the 1,2-shift is the lowest energy fluxional process, while the B3LYP/BS1 energetics (where BS1 = H, C, O: 6-31G(d′); M: mod-LANL2DZ(f)-ECP) indicate the 1,3-shift having a lower electronic energy of activation than the 1,2-shift by 2.9 kcal mol−1. Notably, PBE0/BS1 describes the (CO)3 rotation to be the lowest energy process, followed by the 1,3-shift. Six transition states have been identified in the fluxional processes of each of the (TMCOT)M(CO)3 complexes (except for (TMCOT)W(CO)3), two of which are 1,2-shift transition states. The lowest-energy fluxional process of each (TMCOT)M(CO)3 complex (computed with the PBE0 functional) has a ΔG‡ of 12.6, 12.8, and 13.2 kcal mol−1 for Cr, Mo, and W complexes, respectively. Good agreement was observed between the experimental and computed 1H-NMR and 13C-NMR chemical shifts for (TMCOT)Cr(CO)3 and (TMCOT)Mo(CO)3 at three different temperature regimes, with coalescence of chemically equivalent groups at higher temperatures.

THE H2NO POTENTIAL ENERGY SURFACE EXPLORED WITH HIGH LEVEL AB INITIO AND DENSITY FUNCTIONAL THEORY METHODS

2007 ◽  
Vol 06 (03) ◽  
pp. 549-562
Author(s):  
ABRAHAM F. JALBOUT
Keyword(s):  
Density Functional Theory ◽  
Potential Energy ◽  
Potential Energy Surface ◽  
Density Functional ◽  
Energy Surface ◽  
Hybrid Methods ◽  
Transition States ◽  
Basis Set ◽  
Functional Theory ◽  
High Level

The transition states for the H 2 NO decomposition and rearrangements mechanisms have been explored by the CBS-Q method or by density functional theory. Six transition states were located on the potential energy surface, which were explored with the Quadratic Complete Basis Set (CBS-Q) and Becke's one-parameter density functional hybrid methods. Interesting deviations between the CBS-Q results and the B1LYP density functional theory lead us to believe that further study into this system is necessary. In the efforts to further assess the stabilities of the transition states, bond order calculations were performed to measure the strength of the bonds in the transition state.

Nonnuclear Maxima in the Charge Density

1993 ◽  
Vol 48 (1-2) ◽  
pp. 127-133 ◽  
Author(s):  
Kenneth E. Edgecombe ◽  
Vedene H. Smith, Jr. ◽  
Florian Müller-Plathe
Keyword(s):  
Charge Density ◽  
Electron Density ◽  
Electron Correlation ◽  
Basis Set ◽  
Valence Shell ◽  
Correlation Effects ◽  
Electron Correlation Effects

Abstract Basis-set and electron-correlation effects on the appearance and disappearance of nonnuclear maxima in the electron density are examined in Li2 , Na2 , Na4 and Na5 . It is shown that nonnuclear attractors can be removed in all cases except Li2 . The appearance of a pseudoatom in a lithium molecule correlates remarkably well with the size of the region, in an atomic calculation, of V2r(r) for the valence shell of the atom. This and the fact that the pseudoatom is also present in the promolecule indicate that the pseudoatoms are remnants of, or in fact are portions of, atoms that are not perturbed enough in the molecule to remove an essentially atomic characteristic.

Etude théorique de la structure et de la réactivité de l'anion du pentazole

1983 ◽  
Vol 61 (7) ◽  
pp. 1435-1439 ◽  
Author(s):  
Minh-Tho Nguyen ◽  
Michel Sana ◽  
Georges Leroy ◽  
Jose Elguero
Keyword(s):  
Molecular Nitrogen ◽  
Activation Energies ◽  
Basis Set ◽  
Etude Théorique ◽  
Mo Calculations ◽  
Étude Théorique ◽  
Azide Ion ◽  
Synthetic Target ◽  
Stable Structures

"Abinitio" LCAO-SCF-MO calculations using the 4-31G basis set were carried out in order to study the supersystem [Formula: see text]. The three possible stable structures (azide ion + molecular nitrogen, pentazene ion, and pentazole ion) and their reactions paths were calculated. The pentazole anion is less stable than the reagents [Formula: see text], but much more stable than the pentazene anion; it could constitute a reasonable synthetic target. The activation energies of the different paths were compared with those of the neutral supersystem N5H.

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