scholarly journals Multiconfigurational Static and Dynamic Calculations Explain Tricyclo[4,2,0,02,5]octa-3,7-diene Photochemistry

2020 ◽  
Author(s):  
Jingbai Li ◽  
Steven Lopez
Keyword(s):  
Minimum Energy ◽  
Photochemical Reactions ◽  
Basis Set ◽  
Strained Molecules ◽  
Complete Active Space ◽  
Vertical Excitation ◽  
Active Space ◽  
Ring Opening Reaction ◽  
Self Consistent Field ◽  
Surface Scan

<p>Sunlight is a renewable energy source that can be stored in chemical bonds using photochemical reactions. The synthesis of exotic and strained molecules is especially attractive with photochemical techniques because of the associated efficient and mild reaction conditions. We have used complete active space self-consistent field (CASSCF) calculations with an (8,7) active space and the ANO-S-VDZP basis set to understand the photophysics and subsequent photochemistry of a possible cubane precursor tricyclo[4,2,0,0<sup>2,5</sup>]octa-3,7-diene (<b>1</b>). The energies were corrected with a second-order perturbative correction CASPT2(8,7)/ANO-S-VDZP. The S<sub>0</sub>→S<sub>1</sub> vertical excitation energy of <b>1</b> is 6.25 eV, whose nature is π→π<sup>*</sup> excitation. The minimum energy path from the S<sub>1</sub> Franck-Condon point leads directly to a 4π-disrotatory electrocyclic ring-opening reaction to afford bicyclo[4,2,0]octa-2,4,7-triene. The 2D potential energy surface scan located a rhomboidal S<sub>1</sub>/S<sub>0</sub> minimum energy crossing point that connects <b>1</b> and cubane, suggesting that a cycloaddition is theoretically possible. We used the fewest switches surface hopping to study this reaction: 85% of 1,722 trajectories relaxed to 8 products; the major products are bicyclo[4,2,0]octa-2,4,7-triene (30%) and cycloocta-1,3,5,7-tetraene (32%). Only 0.4% of trajectories undergo a [2+2] cycloaddition to form cubane.<i></i></p>

scholarly journals Multiconfigurational Static and Dynamic Calculations Explain Tricyclo[4,2,0,02,5]octa-3,7-diene Photochemistry

2020 ◽  
Author(s):  
Jingbai Li ◽  
Steven Lopez
Keyword(s):  
Minimum Energy ◽  
Photochemical Reactions ◽  
Basis Set ◽  
Strained Molecules ◽  
Complete Active Space ◽  
Vertical Excitation ◽  
Active Space ◽  
Ring Opening Reaction ◽  
Self Consistent Field ◽  
Surface Scan

<p>Sunlight is a renewable energy source that can be stored in chemical bonds using photochemical reactions. The synthesis of exotic and strained molecules is especially attractive with photochemical techniques because of the associated efficient and mild reaction conditions. We have used complete active space self-consistent field (CASSCF) calculations with an (8,7) active space and the ANO-S-VDZP basis set to understand the photophysics and subsequent photochemistry of a possible cubane precursor tricyclo[4,2,0,0<sup>2,5</sup>]octa-3,7-diene (<b>1</b>). The energies were corrected with a second-order perturbative correction CASPT2(8,7)/ANO-S-VDZP. The S<sub>0</sub>→S<sub>1</sub> vertical excitation energy of <b>1</b> is 6.25 eV, whose nature is π→π<sup>*</sup> excitation. The minimum energy path from the S<sub>1</sub> Franck-Condon point leads directly to a 4π-disrotatory electrocyclic ring-opening reaction to afford bicyclo[4,2,0]octa-2,4,7-triene. The 2D potential energy surface scan located a rhomboidal S<sub>1</sub>/S<sub>0</sub> minimum energy crossing point that connects <b>1</b> and cubane, suggesting that a cycloaddition is theoretically possible. We used the fewest switches surface hopping to study this reaction: 85% of 1,722 trajectories relaxed to 8 products; the major products are bicyclo[4,2,0]octa-2,4,7-triene (30%) and cycloocta-1,3,5,7-tetraene (32%). Only 0.4% of trajectories undergo a [2+2] cycloaddition to form cubane.<i></i></p>

scholarly journals A Theoretical Stereoselectivity Model of Photochemical Denitrogenations of Diazoalkanes Towards Strained 1,3-Dihalogenated Bicyclobutanes

2020 ◽  
Author(s):  
Jingbai Li ◽  
Rachel Stein ◽  
Steven Lopez
Keyword(s):  
Minimum Energy ◽  
Photochemical Reactions ◽  
Basis Set ◽  
Strained Molecules ◽  
Complete Active Space ◽  
Active Space ◽  
Self Consistent Field ◽  
Shoulder Region ◽  
Highly Strained ◽  
Diastereomeric Excess

<p>Photochemical reactions exemplify ‘green’ chemistry and are essential for synthesizing highly strained molecules with mild conditions with light. The light-promoted denitrogenation of bicyclic azoalkanes affords functionalized, stereoenriched bicyclo[1.1.0]butanes. We revisited these reactions with multireference calculations and non-adiabatic molecular dynamics (NAMD) simulations for a series of diazabicyclo[2.1.1]hexenes to predict the photophysics, reactivities, and stereoselectivities. We used complete active space self-consistent field (CASSCF) calculations with an (8,8) active space and ANO-S-VDZP basis set; the CASSCF energies were corrected with CASPT2(8,8)/ANO-S-VDZP. The excitation is consistently n→π* and ranges from 3.77–3.91 eV for the diazabicyclo[2.1.1]hexenes. Minimum energy path calculations showed stepwise C–N bond breaking and led to a minimum energy crossing point, which favors the stereochemical ‘double inversion’ bicyclobutane product. Wigner sampling of <b>1</b> provided Franck-Condon points for 692 NAMD trajectories. We identified competing complete stereoselective and stereochemical scrambling pathways. The stereoselective pathways feature concerted bicyclobutane inversion and N<sub>2</sub> extrusion. The stereochemical scrambling pathways involve N<sub>2</sub> extrusion followed by bicyclobutane planarization, leading to non-stereoselective outcomes. The predicted diastereomeric excess almost exactly match experiment (calc<i>.d.e.</i>=46% <i>vs.</i> exp<i>.d.e.</i>=47%). Our NAMD simulations with 672, 568, and 596 trajectories for <b>1-F</b>, <b>1-Cl</b>, and <b>1-Br</b> predicted diastereomeric excess (<i>d.e.</i>) of 94–97% for the double inversion products. Halogenation significantly perturbs the potential energy surface (PES) towards the retention products because of powerful hyperconjugative interactions. The n<sub>C</sub>→σ<sup>*</sup><sub>C–X</sub>,<sub> </sub>X = F, Cl, Br hyperconjugative interaction leads to a broadened shoulder region on the PES for double inversion.</p>

scholarly journals A Theoretical Stereoselectivity Model of Photochemical Denitrogenations of Diazoalkanes Towards Strained 1,3-Dihalogenated Bicyclobutanes

2020 ◽  
Author(s):  
Jingbai Li ◽  
Rachel Stein ◽  
Steven Lopez
Keyword(s):  
Minimum Energy ◽  
Photochemical Reactions ◽  
Basis Set ◽  
Strained Molecules ◽  
Complete Active Space ◽  
Active Space ◽  
Self Consistent Field ◽  
Shoulder Region ◽  
Highly Strained ◽  
Diastereomeric Excess

<p>Photochemical reactions exemplify ‘green’ chemistry and are essential for synthesizing highly strained molecules with mild conditions with light. The light-promoted denitrogenation of bicyclic azoalkanes affords functionalized, stereoenriched bicyclo[1.1.0]butanes. We revisited these reactions with multireference calculations and non-adiabatic molecular dynamics (NAMD) simulations for a series of diazabicyclo[2.1.1]hexenes to predict the photophysics, reactivities, and stereoselectivities. We used complete active space self-consistent field (CASSCF) calculations with an (8,8) active space and ANO-S-VDZP basis set; the CASSCF energies were corrected with CASPT2(8,8)/ANO-S-VDZP. The excitation is consistently n→π* and ranges from 3.77–3.91 eV for the diazabicyclo[2.1.1]hexenes. Minimum energy path calculations showed stepwise C–N bond breaking and led to a minimum energy crossing point, which favors the stereochemical ‘double inversion’ bicyclobutane product. Wigner sampling of <b>1</b> provided Franck-Condon points for 692 NAMD trajectories. We identified competing complete stereoselective and stereochemical scrambling pathways. The stereoselective pathways feature concerted bicyclobutane inversion and N<sub>2</sub> extrusion. The stereochemical scrambling pathways involve N<sub>2</sub> extrusion followed by bicyclobutane planarization, leading to non-stereoselective outcomes. The predicted diastereomeric excess almost exactly match experiment (calc<i>.d.e.</i>=46% <i>vs.</i> exp<i>.d.e.</i>=47%). Our NAMD simulations with 672, 568, and 596 trajectories for <b>1-F</b>, <b>1-Cl</b>, and <b>1-Br</b> predicted diastereomeric excess (<i>d.e.</i>) of 94–97% for the double inversion products. Halogenation significantly perturbs the potential energy surface (PES) towards the retention products because of powerful hyperconjugative interactions. The n<sub>C</sub>→σ<sup>*</sup><sub>C–X</sub>,<sub> </sub>X = F, Cl, Br hyperconjugative interaction leads to a broadened shoulder region on the PES for double inversion.</p>

scholarly journals Correction to “Variational Relativistic Two-Component Complete-Active-Space Self-Consistent Field Method”

2020 ◽  
Vol 16 (5) ◽  
pp. 3445-3445
Author(s):  
Andrew J. Jenkins ◽  
Hongbin Liu ◽  
Joseph M. Kasper ◽  
Michael J. Frisch ◽  
Xiaosong Li
Keyword(s):  
Field Method ◽  
Complete Active Space ◽  
Active Space ◽  
Consistent Field ◽  
Two Component ◽  
Self Consistent ◽  
Self Consistent Field

Spin–orbit ab initio investigation of the UV photoinduced bond cleavage in iodotrimethylstannane

2009 ◽  
Vol 87 (7) ◽  
pp. 1006-1012 ◽  
Author(s):  
N. Ben Amor ◽  
C. Daniel
Keyword(s):  
Ab Initio ◽  
Bond Cleavage ◽  
Ionic Species ◽  
Spin Orbit ◽  
Complete Active Space ◽  
Active Space ◽  
Consistent Field ◽  
Primary Products ◽  
Self Consistent Field ◽  
Electronic Ground

The photoinduced homolytic cleavage of the Sn–I bond in iodotrimethylstannane (CH3)3SnI, observed after UV irradiation, is investigated by means of spin–orbit ab initio calculations based on CASSCF (complete active space self-consistent field) and MS-CASPT2 (multi-state complete active space 2nd order perturbation theory) methods. The absorption electronic spectrum is characterized by ten low-lying 1,3A′ and 1,3A″ spin eigenstates corresponding to py(I),px(I) → σ*SnI; σSnI → σ*SnI and py(Sn), px(Sn) → σ*SnI, where σSnI and σ*SnI are the bonding and anti-bonding orbitals of the Sn–I bond along the pz axis. From the 1A′ electronic ground state and these ten spin eigenstates, 21 spin–orbit states are generated leading to various deactivation channels of (CH3)3SnI, corresponding to the formation of radicals (CH3)3Sn• and •I and to the ionic species (CH3)3Sn+ and I–. Irradiation into the upper band at 175 nm should lead to the heterolytic cleavage of the Sn–I bond to form the ionic primary products exclusively, whereas absorption into the shoulder at 250 nm induces the homolytic breaking with formation of the radical products.

The ground state and low-lying excited states of CCCN radical and its ions: a CASSCF/CASPT2 study

2016 ◽  
Vol 94 (9) ◽  
pp. 803-807
Author(s):  
Angyang Yu
Keyword(s):  
Excited States ◽  
Ground State ◽  
Linear Structure ◽  
Electronic Configuration ◽  
Geometric Optimization ◽  
Oscillator Strengths ◽  
Basis Set ◽  
Excitation Energies ◽  
Complete Active Space ◽  
Vertical Excitation

The ground state and low-lying excited states of the CCCN radical and its ions have been investigated systematically using the complete active space self-consistent field (CASSCF) and multi-configuration second-order perturbation theory (CASPT2) methods in conjunction with the ANO-RCC-TZP basis set. The calculated results show that the state 12Σ+ has the lowest CASPT2 energy among the electronic states. By means of the geometric optimization of this radical, it could be found that the molecule exhibits linear structure, with the bond lengths R1 = 1.214 Å, R2 = 1.363 Å, R3 = 1.162 Å, which are very close to the experimental values. The calculated vertical excitation energies and the corresponding oscillator strengths show that there are three relatively strong peaks at energies 0.63, 4.04, and 5.49 eV, which correspond to the transitions 12Σ+ → 12Π, 12Σ+ → 22Π, and 12Σ+ → 22Σ+, respectively. Additionally, the electronic configuration and the harmonic vibration frequencies of each state are also investigated.

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