Dimethyldioxirane, Carbonyl Oxide, and the Transition State Connecting Them:  Electronic Structures, Relative Energies, and Vibrational Frequencies

2000 ◽  
Vol 104 (33) ◽  
pp. 7892-7897 ◽  
Author(s):  
Seung-Joon Kim ◽  
Henry F. Schaefer
Keyword(s):  
Transition State ◽  
Electronic Structures ◽  
Vibrational Frequencies ◽  
Carbonyl Oxide

scholarly journals Decomposition of d- and f-Shell Contributions to Uranium Bonding from the Quantum Theory of Atoms in Molecules: Application to Uranium and Uranyl Halides

Inorganics ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 88 ◽  
Author(s):  
Jonathan Tanti ◽  
Meghan Lincoln ◽  
Andy Kerridge
Keyword(s):  
Quantum Theory ◽  
Electronic Structures ◽  
Density Functional ◽  
Covalent Bond ◽  
Vibrational Frequencies ◽  
Atoms In Molecules ◽  
High Symmetry ◽  
Strong Correlations ◽  
Bond Stability ◽  
Fluoride Ligands

The electronic structures of a series of uranium hexahalide and uranyl tetrahalide complexes were simulated at the density functional theoretical (DFT) level. The resulting electronic structures were analyzed using a novel application of the Quantum Theory of Atoms in Molecules (QTAIM) by exploiting the high symmetry of the complexes to determine 5f- and 6d-shell contributions to bonding via symmetry arguments. This analysis revealed fluoride ligation to result in strong bonds with a significant covalent character while ligation by chloride and bromide species resulted in more ionic interactions with little differentiation between the ligands. Fluoride ligands were also found to be most capable of perturbing an existing electronic structure. 5f contributions to overlap-driven covalency were found to be larger than 6d contributions for all interactions in all complexes studied while degeneracy-driven covalent contributions showed significantly greater variation. σ-contributions to degeneracy-driven covalency were found to be consistently larger than those of individual π-components while the total π-contribution was, in some cases, larger. Strong correlations were found between overlap-driven covalent bond contributions, U–O vibrational frequencies, and energetic stability, which indicates that overlap-driven covalency leads to bond stabilization in these complexes and that uranyl vibrational frequencies can be used to quantitatively probe equatorial bond covalency. For uranium hexahalides, degeneracy-driven covalency was found to anti-correlate with bond stability.

Transition state dynamics and a QM/MM model for the Cl– + C2H5Cl SN2 reaction

2004 ◽  
Vol 82 (6) ◽  
pp. 891-899 ◽  
Author(s):  
Lipeng Sun ◽  
Eunkyung Chang ◽  
Kihyung Song ◽  
William L Hase
Keyword(s):  
Hydrogen Atom ◽  
Transition State ◽  
Reaction Dynamics ◽  
Vibrational Frequencies ◽  
Dynamics Simulation ◽  
Rrkm Theory ◽  
Direct Dynamics ◽  
Sn2 Reaction ◽  
Classical Trajectories ◽  
Link Atom

A MP2/6-31G* direct dynamics simulation is used to study the dynamics of the central barrier [Cl-C2H5-Cl]– for the Cl– + C2H5 SN2 reaction. The majority of the trajectories move off the central barrier to form the Cl––C2H5Cl complex and appear to undergo efficient IVR as assumed by RRKM theory. However, some of the trajectories move directly to products without forming the complex, a non-RRKM result. A hydrogen atom link-atom QM/MM model is described for studying the dynamics of [X-CH2R-Y]– central barriers with the -R substituent. The model is used to calculate vibrational frequencies for the [Cl-C2H5-Cl]– central barrier.Key words: SN2 reaction dynamics, RRKM theory, QM/MM model, central barrier dynamics, direct dynamics classical trajectories.

scholarly journals Computational Study of Electronic Influence of Guanidine Substitution on Diels-Alder Reactions of Heterocyclic Dienes

2019 ◽  
Vol 92 (2) ◽  
pp. 279-286
Author(s):  
Ivana Antol ◽  
Luka Barešić ◽  
Zoran Glasovac ◽  
Davor Margetić
Keyword(s):  
Transition State ◽  
Quantum Chemical Calculations ◽  
Electronic Structures ◽  
Quantum Chemical ◽  
Computational Study ◽  
Cycloaddition Reaction ◽  
Diels Alder ◽  
Reaction Barriers ◽  
Reactivity Order

Quantum-chemical calculations of cycloaddition properties of cyclic heterodienes substituted with guanidine functionality were carried out. Molecular and electronic structures of series of dienes (pyrrole, furan, thiophene, isoindole and 1,3-butadiene) were calculated and reactivity order established on the basis of FMO theory. Transition state calculations of model [4+2] cycloaddition reaction with acetylene indicate that guanidine substitution influences reaction barriers in moderate extent (up to ~4 kcal mol–1). The substitution position plays an important role on the sign and magnitude of the effect and protonation of nitrogen possessing substituents increases reactivity of dienes.

Transition-state electronic structures in SN2 reactions

1989 ◽  
Vol 111 (5) ◽  
pp. 1575-1579 ◽  
Author(s):  
Zheng Shi ◽  
Russell J. Boyd
Keyword(s):  
Transition State ◽  
Electronic Structures ◽  
Sn2 Reactions

Transition state structure, barrier height, and vibrational frequencies for the reaction Cl+CH4→CH3+HCl

1989 ◽  
Vol 90 (12) ◽  
pp. 7137-7142 ◽  
Author(s):  
Thanh N. Truong ◽  
Donald G. Truhlar ◽  
Kim K. Baldridge ◽  
Mark S. Gordon ◽  
Rozeanne Steckler
Keyword(s):  
Transition State ◽  
Barrier Height ◽  
Vibrational Frequencies ◽  
State Structure ◽  
Transition State Structure

On the structure of S42+ and its formation from 2S2+•Ab initio SCF and CASSCF studies

1994 ◽  
Vol 72 (2) ◽  
pp. 298-303 ◽  
Author(s):  
Mousumi Sannigrahi ◽  
Friedrich Grein
Keyword(s):  
Transition State ◽  
Ab Initio ◽  
Minimum Energy ◽  
Vibrational Frequencies ◽  
Square Planar ◽  
Experimental Values ◽  
Minimum Energy Paths

Ab initio studies up to the MP2/6-31G* level were performed on the geometry and energy of S42+. Eleven different structures were considered. In the RHF/6-31G* method, the square structure is the most stable, followed by the trans-planar C2h structure. S42+ (square) is 105.9 kcal/mol less stable than 2S22+. Minimum energy paths were calculated for the reaction 2S2+ → S42+, both in C2v and D2h symmetry. Using RHF/6-31G*, the transition state lies about 50 kcal/mol above the energy of square planar S42+. Using CASSCF or MP2 methods this energy can be significantly lowered (to about 33 kcal/mol in MP2/6-31G*). Calculated vibrational frequencies for the square structure are also given and compared with experimental values.

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