Theoretical Evaluation of Alternative Pathways in the Stevens Rearrangement

1995 ◽  
Vol 48 (8) ◽  
pp. 1413 ◽  
Author(s):  
GL Heard ◽  
BF Yates
Keyword(s):  
Free Radical ◽  
Single Point ◽  
Computational Cost ◽  
Polarizable Continuum Model ◽  
Orbital Theory ◽  
Theoretical Evaluation ◽  
Stevens Rearrangement ◽  
Alternative Pathways ◽  
Semi Empirical ◽  
Polarizable Continuum

Ab initio and semi-empirical molecular orbital theory has been used to explore the ion-pair and lithium-catalysed pathways in the Stevens rearrangement of an alkylammonium ylide to an amine. These pathways represent alternatives to the concerted and free radical mechanisms which we have previously studied. Solvation effects have been included via a polarizable continuum model. Finally, the calculations have been extended to a set of experimentally observable compounds. For the nine systems studied here, the stepwise free radical pathway is predicted in every case to be the favourable mechanism for the Stevens rearrangement. Single-point MP2/6-31G(d) calculations on fully optimized PM3 geometries are shown to provide a useful method of including electron correlation at low computational cost.

A Theoretical Study of the Stevens Rearrangement of Methylammonium Methylide and Methylammonium Formylmethylide

1993 ◽  
Vol 46 (9) ◽  
pp. 1375 ◽  
Author(s):  
GL Heard ◽  
KE Frankcombe ◽  
BF Yates
Keyword(s):  
Free Radical ◽  
Theoretical Study ◽  
Energy Difference ◽  
Reaction Pathways ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Radical Process ◽  
Stevens Rearrangement ◽  
Semi Empirical ◽  
Free Radical Process

Ab initio and semi-empirical molecular orbital theory has been used to study the reaction pathways of the Stevens rearrangement of the prototype methylammonium methylide and methylammonium formylmethylide . For both reactions, the stepwise (free radical) process is predicted to require less energy than the concerted rearrangement (in accordance with experimental suggestions). With inclusion of electron correlation, the energy difference between these pathways is reduced; however, for the smaller system at the CCSD/6-31G(d) level of theory, the free radical process is still favoured by over 180 kJ mol-1. For both systems, the concerted transition structures for the pericyclic mechanisms reveal that some amount of bonding is retained in these formally symmetry-forbidden processes.

Modeling of a Rotaxane-based Molecular Device

2002 ◽  
Vol 741 ◽  
Author(s):  
Xiange Zheng ◽  
Karl Sohlberg
Keyword(s):  
Single Point ◽  
Computational Cost ◽  
Geometry Optimization ◽  
Potential Energy Function ◽  
Computational Procedure ◽  
Structural Features ◽  
Full Geometry Optimization ◽  
Point Energy ◽  
Semi Empirical ◽  
Relationship Of

ABSTRACTA computational procedure is presented for investigating photo-induced switchable rotaxanes and demonstrated for a known system. This procedure starts with the generation of more than 104 chemically reasonable rotaxane conformations based on an empirical intramolecular potential energy function. Single-point energy calculations at the semi-empirical (AM1) level are carried out for each structure in the singlet (ground), triplet, and anionic doublet states. The structural features are assigned and then correlated with energy for each state. What emerges is a profile of the structure-energy relationship that captures the salient features of the system that endow it with device-like character. Full geometry optimization of a subset of co-conformations (∼1%) demonstrates that the procedure based on single-point calculations is sufficient to obtain a profile of the relationship of structural features to energy that is consistent with experiments, at greatly reduced computational cost.

SOLVENT EFFECTS OF KINETICS OF [1,5] H-SHIFT IN CYCLOPENTADIENE AND ITS DERIVATIVES

2005 ◽  
Vol 04 (01) ◽  
pp. 151-161 ◽  
Author(s):  
VUDHICHAI PARASUK ◽  
SAKULSUK UNARUNOTAI
Keyword(s):  
Solvent Effects ◽  
Single Point ◽  
Solvent Polarity ◽  
Polarizable Continuum Model ◽  
Activation Energies ◽  
Free Energies ◽  
Solvent Systems ◽  
Polarizable Continuum ◽  
Kinetics Of ◽  
Fluoro Derivatives

Geometries of reactants, products (in the case of fluoro derivatives), and transition states in gas and solution phases of [1,5] H-shift of cyclopentadiene and 2-fluorocyclo-pentadiene were optimized using B3LYP/6-31++G(d,p) . The solvent effects were included using the Polarizable Continuum Model (PCM). Four solvent systems i.e. chloroform, dichloromethane, diethylether, and methanol, were considered. For cyclopentadiene, single point MP2/6-31++G(d,p) were also carried out. For cyclopentadiene and 2-fluorocyclopentadiene, using B3LYP/6-31++G(d,p) activation free energies of 25.47 and 28.74 kcal/mol respectively were yielded for the reaction in vacuum. In solutions, calculated activation energies for the reaction are slightly decreased with the reduction of around 0.5–3 kcal/mol depending on solvent. Good correlation between the solvent polarity and activation energies was also observed. Thus, the [1.5] H-shift in cyclopentadiene and its derivatives could be enhanced in polar solvents.

Achieving linear-scaling computational cost for the polarizable continuum model of solvation

2004 ◽  
Vol 111 (2-6) ◽  
pp. 90-100 ◽  
Author(s):  
Giovanni Scalmani ◽  
Vincenzo Barone ◽  
Konstantin N. Kudin ◽  
Christian S. Pomelli ◽  
Gustavo E. Scuseria ◽  
...  
Keyword(s):  
Continuum Model ◽  
Computational Cost ◽  
Polarizable Continuum Model ◽  
Linear Scaling ◽  
Polarizable Continuum

Modeling of a Rotaxane-based Molecular Device

2002 ◽  
Vol 761 ◽  
Author(s):  
Xiange Zheng ◽  
Karl Sohlberg
Keyword(s):  
Single Point ◽  
Computational Cost ◽  
Geometry Optimization ◽  
Potential Energy Function ◽  
Computational Procedure ◽  
Structural Features ◽  
Full Geometry Optimization ◽  
Point Energy ◽  
Semi Empirical ◽  
Relationship Of

ABSTRACTA computational procedure is presented for investigating photo-induced switchable rotaxanes and demonstrated for a known system. This procedure starts with the generation of more than 104 chemically reasonable rotaxane conformations based on an empirical intramolecular potential energy function. Single-point energy calculations at the semi-empirical (AM1) level are carried out for each structure in the singlet (ground), triplet, and anionic doublet states. The structural features are assigned and then correlated with energy for each state. What emerges is a profile of the structure-energy relationship that captures the salient features of the system that endow it with device-like character. Full geometry optimization of a subset of co-conformations (∼1%) demonstrates that the procedure based on single-point calculations is sufficient to obtain a profile of the relationship of structural features to energy that is consistent with experiments, at greatly reduced computational cost.

scholarly journals Substituent and Solvent Effects on the Electronic and Structural Properties of Silacyclopropylidenoids

2017 ◽  
Vol 59 (1) ◽  
Author(s):  
Akin Azizoglu
Keyword(s):  
Electrostatic Potential ◽  
Continuum Model ◽  
Molecular Electrostatic Potential ◽  
Single Point ◽  
Polarizable Continuum Model ◽  
Frontier Molecular Orbitals ◽  
Polarizable Continuum ◽  
Isomeric Structures ◽  
Molecular Electrostatic Potential Maps ◽  
Electronic And Structural Properties

The isomeric structures, energies, and properties of the substituted silacyclopropylidenoids, SiC<sub>2</sub>H<sub>3</sub>RLiBr (R= –H, –CH<sub>3</sub>, –SiH<sub>3</sub>, –CN, –OH, –NH<sub>2</sub>), were studied by <em>ab initio</em> calculations at the MP2/6-311+G(d,p) level of theory. The calculations indicate that each of SiC<sub>2</sub>H<sub>3</sub>RLiBrs for R= –H, –CH<sub>3</sub>, –SiH<sub>3</sub>, –CN, –OH, –NH<sub>2 </sub>has three stationary structures: silacyclopropylidenoid (<strong>S</strong>), tetrahedral (<strong>T1</strong> or <strong>T2</strong>), and inverted (<strong>I</strong>). The conductor–like polarizable continuum model (CPCM) using various solvents (dimethyl sulfoxide (ε = 46.7), acetone (ε = 21.0), tetrahydrofuran (ε = 7.5), and diethyl ether (ε = 4.3)) has been applied to compute single point energies for title molecules. In addition, the molecular electrostatic potential maps, natural bond orbitals, and the frontier molecular orbitals of substituted silacyclopropylidenoids were calculated.

scholarly journals Interface of the Polarizable Continuum Model of Solvation with Semi-Empirical Methods in the GAMESS Program

PLoS ONE ◽  
2013 ◽  
Vol 8 (7) ◽  
pp. e67725 ◽  
Author(s):  
Casper Steinmann ◽  
Kristoffer L. Blædel ◽  
Anders S. Christensen ◽  
Jan H. Jensen
Keyword(s):  
Continuum Model ◽  
Polarizable Continuum Model ◽  
Empirical Methods ◽  
Semi Empirical ◽  
Polarizable Continuum

scholarly journals THEORETICAL EVALUATION OF THE PERMEABILITY OF DISCHARGE ITEM (LiOOH) IN Li-O2 BATTERIES

2021 ◽  
Vol 51 (3) ◽  
pp. 153-157
Author(s):  
Abrar Ul Hassan ◽  
Cihat Guleryuz
Keyword(s):  
Natural Bond Orbital ◽  
Polarizable Continuum Model ◽  
Solvation Model ◽  
Lithium Ions ◽  
Theoretical Evaluation ◽  
Solvation Energies ◽  
Ft Ir ◽  
Polarizable Continuum ◽  
Ft Raman ◽  
Medium Influence

Both lithium ions and protons have been directly implicated in oxygen reduction and evolutionary responses and lithium hydroperoxide and lithium hydroxide are recognized as prevailing discharge ingredients. Attributes of lithium hydroperoxide shall be evaluated in principle. Impressively, the reaction of lithium hydroperoxide to triiodide shows quicker material properties, which allows a slightly lower excessive-potential during the charging cycle. The frontier molecular orbitals (FMOs), UV-Vis, and solvation model-based studies remained unknown. Therefore, we intended to study the Reaction path study, natural bond orbital, FMOs, UV-VIS, thermodynamic properties and medium influence on solvation energies, dipole moment, FT-IR and FT-Raman using polarizable continuum model (PCM) and density-based solvation model (SMD). The electronic properties of the molecule were calculated by M06-2X/6-31G (d,P) and B3LYP/6-31G (d,p) level of theories. Natural bond orbital discloses that the optimum stabilization energy managed to reach 39.64 kJ / mol, which is accountable for the extra stability of the compound. Based on materials impacts on FT-IR and FT-Raman intensities are identified in the understudy compound. Frequencies improved from gas to the solvent process.

Sign in / Sign up

Export Citation Format

Share Document