DFT Calculations and NBO Analysis of 2-Chloroethylethyldichlorosilane Unimolecular Elimination Kinetics in the Gas Phase

Ab initio molecular orbital calculations have been used to investigate the thermal decomposition kinetics of 2-chloroethylethyldichlorosilane at the B3LYP/6-311+G**,B3PW91/6-311+G**,and MPW1PW91/6-311+G** levels of theory.Among these methods,the results(activation parameters) obtained using the B3LYP/6-311+G** level are in good agreement with the available experimental data.The calculated data imply that in the unimolecular β-elimination reactions of the studied compound in the gas phase,the polarization of C(1)-Cl(3) and C(1)-H(4) bonds in the sense of C(1)δ+-Cl(3)δ-and C(1)δ+-H(4)δ-,respectively,is a determining factor in the gas phase elimination reactions 1,2 and 3.Analysis of bond order,natural bond orbital charges,bond indexes,synchro-nicity parameters,and IRC calculations suggest the elimination of 2-chloroethylethyldichlorosilane via reactions 1～3 can be described as concerted and slightly asynchronous.The transition state structures of these reactions are a four-membered cyclic structure.     

一氟二氯代甲烷热解离动力学的理论研究

利用从头算和ＲＲＫＭ理论研究了一氟二氯代甲烷热解离动力学，并得到了一套热力学和动力学参数。研究了三种不同的解离通道：（１）ＨＣｌ＋ＣＦＣｌ_２，（２）Ｃｌ＋ＣＨＦＣｌ，（３）ＨＦ＋ＣＣｌ_２，它们的活化能分别为：２４３．３、２５８．９、３０９．８ｋＪ／ｍｏｌ。研究结果表明，氯化氢消除反应和碳氯键简单断键反应是两个主要的并且是竞争的通道，三个反应通道的高压速率常数分别为ｋ_１＝８．７４×１０~（１４）ｅｘｐ（－２９１６３Ｔ）_ｓ~（－１），ｋ_２＝７．０９×１０~（１５）ｅｘｐ（－３１１２１／Ｔ）_ｓ~（－１），Ｒ_３＝３．８７×１０~（１１）ｅｘｐ（－３７０３９／Ｔ）_ｓ~（－１），它们都具有明显的温度和压力依赖关系。     

Configurational and Conformational Properties of 1,3,7,9-Tetraphospha-Cyclododeca-1,2,7,8-tetraene: An Ab Initio Study and NBO Analysis

An investigation employing the ab initio molecular orbital (MO) and density functional theory (DFT) methods to calculate structural optimization and conformational interconversion pathways for the two diastereoisomeric forms, (±) and meso configurations of 1,3,7,9-tetraphospha-cyclododeca-1,2,7,8-tetraene (1) was undertaken. Two axial symmetrical conformations are found for (±)-1 configuration. (±)-1-TB axial symmetrical form is found to be about 0.35 and 0.99 kcal mol^?1 more stable than (±)-1-Crown axial symmetrical conformation, as calculated by HF/6-31G*//HF/6-31G* and B3LYP/6-31G*//HF/6-31G* levels of theory, respectively. The unsymmetrical meso-1-TBCC form is found to be the most stable geometry, among the various conformations of meso-1 configuration. HF/6-31G*//HF/6-31G* and B3LYP/6-31G*//HF/6-31G* results showed that between the two most stable conformations of (±) and meso configurations, (±)-1-TB is more stable than meso-1-TBCC by about 3.35 and 2.43 kcal mol^?1, respectively. In addition, MP2/6-31G* and B3LYP/6-311+G** results showed that the (±)-1-TB form is about 1.10 and 2.36 kcal mol^?1 more stable than the meso-1-TBCC form. Further, NBO results revealed that in the most stable form of meso configuration (meso-1-TBCC), the sum of the π* allenic antibonding orbital occupancies (Σ π *_occupancy) is greater than dl configuration ((±)-1-TB). Also, NBO results indicated that in the (±)-1-TB conformer, the sum of σ and π allenic moieties bonding orbital deviations (Σ σ _dev+Σ π _dev) from their normal values, is lower than in the meso-1-TBCC form.     

Hybrid-DFT Study and NBO Interpretation of the Configurational Behavior of 2-Halotetrahydrothiopyran S-Oxides

Abstract

Natural bond orbital (NBO) interpretation and hybrid density functional theory (hybrid-DFT: B3LYP/Def2-TZVPP)-based methods were used to investigate the impacts of the generalized anomeric effects (GAE), electrostatic, and steric interactions on the conformational properties of cis and trans isomers of 2-fluoro-, 2-chloro-, and 2-bromotetrahydrothiopyran S-oxide (1–3). The results obtained showed that the trans-axial configurations are the most stable forms of compounds 1–3. Based on the results obtained, the instability of the second lowest energy-minimum (cis-equatorial configuration, with axial S?O and equatorial C?X bonds, X = halogen atoms) increases from compound 1 to compound 3. This trend is also observed for the third lowest energy-minimum (i.e., the trans-equatorial configuration). Contrary to the trend observed for the cis- and trans-equatorial forms, the instability of the cis-axial form compared to the trans-axial form, increases from 1 to 2 but decreases slightly from 2 to 3. The correlations between the GAE, bond orders, steric effects, ΔG, Δμ, structural parameters, and conformational and configurational behaviors of compounds 1–3 have been investigated.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

DFT Study of the Mechanism and Regioselectivity of 1,3-Pentadiene with Methyl Acrylate Using Theoretical Approaches

<正>Ab initio density functional theory (DFT) calculations have been used to study regioselectivity in the Diels-Alder (DA) cycloaddition reaction between 1,3-pentadiene and methyl acrylate. The DFT calculations were performed with the B3LYP functional and 6-311+G~(**) basis set. Two synchronous transition structures corresponding to the formation of different regioisomers associated with the two reaction channels have been located. The DFT calculations generated transition geometries with a very small degree of asynchronicity. The present analysis shows that these reactions have normal electron demand (NED) character. Moreover, the results obtained from energetic and electronic approaches with the exception of Houk's rule confirm that ortho regioisomer is the major product.     

Conformational Behaviors of 2-Substituted Cyclohexanone Oximes: An AB Initio,Hybrid Dft Study,and NBO Interpretation

Abstract

The impacts of the generalized anomeric effect (GAE) and gauche effect (GE) associated with donor–acceptor electron delocalizations and dipole–dipole interactions on the conformational properties of 2-methoxy- (1), 2-methylthio- (2), 2-methylseleno- (3), 2-fluoro- (4), 2-chloro- (5), and 2-bromocyclohexanone oxime (6) have been studied by means of hybrid density functional theory (B3LYP/6–311+G**) and ab initio molecular orbital (HF/6–311+G**)-based methods and natural bond orbital (NBO) interpretation. Both methods used showed that the above compounds exist predominantly in the axial chair conformation and the axial conformation stability increased from 2-methoxy- (1) to 2-methylselenocyclohexanone oxime (3) and also from 2-fluoro- (4) to 2-bromocyclohexanone oxime (6). The NBO analysis showed that the GAE increases from compound 1 to compound 3 and also from compound 4 to compound 6. GE does not have significant impact on the conformational behaviors of compounds 1–6 and GAE succeeds in accounting qualitatively for the increase of the axial preferences in both series of compounds.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental resource: Table S1.

Supporting Information Available. The structures optimized and thermodynamic functions of the axial and equatorial conformations of compounds 1–6. This material is available free of charge via the Internet.     

Ab Initio Study of the Various Pathways of the Decomposition ([2+2]elimination) of 2-Chloroethyltrichlorosilane

Abstract

The decomposition of 2-chloroethyltrichlorosilane (1) to ethylene-tetrachlorosilane (2), hydrogen chloride-ethylenetrichlorosilane (3), and ethylenechloride-trichlorosilane (4) was investigated using ab initio Molecular Orbital (MO) and Density Functional Theory (DFT). Study on the HF/6-31G level of theory revealed that the required energy for the decomposition of compound 1 to 2, 3, and 4 is 59.86, 101.13, and 63.29 kcal mol^?, respectively. MP2/6-31G*//HF/6-31G* calculated barrier height for the decomposition of compound 1 to 2, 3, and 4 is 60.59, 94.04, and 66.91 kcal mol^?1, respectively. Also, B3LYP/6-31G*//HF/6-31G* results indicate that the barrier height for the decomposition of compound 1 to 2, 3, and 4 is 51.71, 85.38, and 53.74 kcal mol^?1, respectively. Among the three methods, which have been used to calculate the barrier height of the decomposition of compound 1 to 2–4, B3LYP/6-31G**//HF/6-31G** is in good agreement with the reported experimental data. Contrary to the previously evaluated experimental values for the decomposition of compoun 1 to 3 and 4, all three methods predict a higher energy barrier for these reactions.     

Thermal Decomposition Kinetics of Ethane Halides and Derivatives（C_2H_（6-n）X_n（n = 1～3）;X = F,Cl,Br）：DFT Study and NBO Analysis

A theoretical study of the thermal decomposition kinetics of ethane halides(C2H6-nXn(n = 1～3);X = F,Cl,Br) has been carried out at the B3LYP/6-31++G** and B3PW91/631++G** levels of theory.Among these methods and comparison of activation parameters with available experimental values,the B3PW91/6-31++G** method is in good agreement with the experimental data.The analysis of bond order and natural bond orbital(NBO) charges,bond indexes,and synchronicity parameters suggest the elimination of HX in reactions 1～9(HF:compounds 1～3,HCl:compounds 4～6,and HBr:compounds 7～9) occur through a concerted and slightly asynchronous four-membered cyclic transition state type of mechanism.     

Theoretical investigation of unimolecular decomposition channels of furan4

Density functional theory and high-level ab initio calculations were carried out to investigate three unimolecular decomposition channels of furan. All equilibrium and transition state structures along the proposed decomposition channels are fully optimized by B3LYP/6-31G** and characterized at the same level of theory by vibrational and intrinsic reaction coordinate analyses. Relative energies of the optimized structures were evaluated at theoretical levels up to QCISD(T)/6-311++G**. The theoretical results suggest that the unimolecular decomposition channel of isoxazole, proposed in an experimental study and implied to be the main decomposition channel of furan, is responsible only for the formation of HC(TRIPLE BOND)CH and H₂O(DOUBLE BOND)C(DOUBLE BOND)O, minor products of furan thermal decomposition. A new decomposition mechanism, proposed in the present study, is shown to be more likely responsible for the formation of CH₃C(TRIPLE BOND)CH and CO, major products of furan thermal decomposition. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 240–249, 1998     

Kinetic Study and NBO Analysis of the Dehydrogenation Mechanism of Five‐membered Ring Heterocyclic 2,5‐Dihydro‐[furan,thiophene, selenophene

The theoretical study of the dehydrogenation of 2,5‐dihydro‐[furan ( 1 ), thiophene ( 2 ), and selenophene ( 3 )] was carried out using ab initio molecular orbital (MO) and density functional theory (DFT) methods at the B3LYP/6‐311G**//B3LYP/6‐311G** and MP2/6‐311G**//B3LYP/6‐311G** levels of theory. Among the used methods in this study, the obtained results show that B3LYP/6‐311G** method is in good agreement with the available experimental values. Based on the optimized ground state geometries using B3LYP/6‐311G** method, the natural bond orbital (NBO) analysis of donor‐acceptor (bond‐antibond) interactions revealed that the stabilization energies associated with the electronic delocalization from non‐bonding lone‐pair orbitals [LP(e)_X3] to δ*_{C(1)  H(2)} antibonding orbital, decrease from compounds 1 to 3 . The LP(e)_X3→δ*_{C(1)  H(2)} resonance energies for compounds 1 – 3 are 23.37, 16.05 and 12.46 kJ/mol, respectively. Also, the LP(e)_X3→δ*_{C(1)  H(2)} delocalizations could fairly explain the decrease of occupancies of LP(e)_X3 non‐bonding orbitals in ring of compounds 1 – 3 ( 3 > 2 > 1 ). The electronic delocalization from LP(e)_X3 non‐bonding orbitals to δ*_{C(1)  H(2)} antibonding orbital increases the ground state structure stability, Therefore, the decrease of LP(e)_X3→δ*_{C(1)  H(2)} delocalizations could fairly explain the kinetic of the dehydrogenation reactions of compounds 1 – 3 (k ₁ >k ₂ >k ₃ ). Also, the donor‐acceptor interactions, as obtained from NBO analysis, revealed that the (_C(4)C(7)→δ*_{C(1)  H(2)} resonance energies decrease from compounds 1 to 3 . Further, the results showed that the energy gaps between (_C(4)C(7) bonding and δ*_{C(1)  H(2)} antibonding orbitals decrease from compounds 1 to 3 . The results suggest also that in compounds 1 – 3 , the hydrogen eliminations are controlled by LP(e)→δ* resonance energies. Analysis of bond order, natural bond orbital charges, bond indexes, synchronicity parameters, and IRC calculations indicate that these reactions are occurring through a concerted and synchronous six‐membered cyclic transition state type of mechanism.     

Reinvestigation of intramolecular hydrogen bond in malonaldehyde derivatives: An ab initio,AIM and NBO study

The RAHB systems in malonaldehyde and its derivatives at MP2/ 6‐311++G(d,p) level of theory were studied and their intramolecular hydrogen bond energies by using the related rotamers method was obtained. The topological properties of electron density distribution in O? H···O intramolecular hydrogen bond have been analyzed in term of quantum theory of atoms in molecules (QTAIM). Correlations between the H‐bond strength and topological parameters are probed. The results of QTAIM clearly showed that the linear correlation between the electron density distribution at HB critical point and RAHB ring critical point with the corresponding hydrogen bond energies was obtained. Moreover, it was found a linear correlation between the electronic potential energy density, V(r_cp), and hydrogen bond energy which can be used as a simple equation for evaluation of HB energy in complex RAHB systems. Finally, the similar linear treatment between the geometrical parameters, such as O···O or O? H distance, and Lp(O)→σ*_OH charge transfer energy with the intramolecular hydrogen bond energy is observed. © 2010 Wiley Periodicals, Inc., Int J Quantum Chem, 2011     

消除KSM能量分解分析中的偶合项

在用KSM方法对分子相互作用能量的分解过程中由于轨道间的相互影响，使分 解的能量各分量之和不等于总的相互作用能，即产生偶合项。用能级位移算符逐步 改变某些特定轨道的能级，可以逐步解除对这些特定轨道的冻结，从而可以减少以 至完全消除轨道间的相互影响，即消除偶合项，使能量分解结果清晰、准确。     

氧气和CS自由基反应势能面的密度泛函理论研究

应用量子化学从头计算和密度泛函理论(DFT)对O_2和CS自由基的反应进行了研 究。在B3LYP/6-311G~(**)水平上计算出了各物种的优化构型、振动频率和零点振 动能(ZPVE)。各物种的总能量由CCSD（T）/6-311G~(**)//B3LYP/6-311G~(**)给出 ，并对总能量进行了零点能校正。计算结果表明：CS自由基中的C端沿着O_2的双键 中线方向进攻，进行加成反应，反应的第一步放出大量的热量(450 kJ/mol)，推动 反应继续进行，从稳定的中间体4(Cs)出发，反应主要通过O的相邻位置的迁移生成 P_1(CO+SO)和P_3(COS+O)；通过S的相邻位置的迁移生成了重要的反应复合物 (complex 1)，进一步离解为产物P_2(CO_2+S)。计算结果可以很好地解释反应机理 。     

NBO,NMR Analysis,and Hybrid DFT Study of Structural and Configurational Properties of Di-tert-butyl-, bis(trimethysilyl)-, Bis(trimethgermyl)-, and Bis(trimethylstannyl)- cyclopenta-1,3-dienes

Abstract

The alkyl 1,2-shift in di-tert-butylcyclopenta-1,3-diene (1) and the metallotropic 1,2-shifts in bis(trimethylsilyl)cyclopenta-1,3-diene (2), bis(trimethylgermyl)cyclopenta-1,3-diene (3), and bis(trimethylstannyl)cyclopenta-1,3-diene (4) have been investigated by means of natural bond orbital (NBO), nuclear magnetic resonance (NMR) analysis, and hybrid density functional theory based methods. The B3LYP/DZVP results showed that the M(CH₃)₃ group [M = C (1), Si (2), Ge (3), and Sn (4)] migration barrier heights around cyclopentadienyl rings decrease from di-tert-butylcyclopenta-1,3-diene to its stannane derivative. Also, based on the results obtained, the stabilities of the 5,5-isomers in comparison to the 1,5- and 2,5-isomers increase from di-tert-butylcyclopenta-1,3-diene to its stannane derivative. The results suggest that in these compounds the metallotropic shifts are controlled by the stabilization energies associated with σ→π* electron delocalizations and the increase of the σ_C5-M→π*_C1-C2 electron delocalizations facilitates the M(CH₃)₃ group migrations around cyclopentadienyl rings. Based on the aromatic stabilization energy (ASE) values calculated, the aromaticity increases from the 5,5-isomers of di-tert-butylcyclopenta-1,3-diene to its stannane derivative but the variation of the nucleus-independent chemical shift, NICS(0) and NICS(1), values calculated are not in accordance with the ASE values calculated and the σ_C5-M→π*_C1-C2

electron delocalizations. The correlations between the sigmatropic shift barrier heights, σ→π* electron delocalizations, ASE, and NICS values were investigated.

GRAPHICAL ABSTRACT     

Theoretical Study of the Unimolecular Decomposition Mechanism of Chloromethanol

The decomposition pathways of chloromethanol have been studied by ab initio calculation. Equilibriums and transition states have been optimized at the UMP2(full)/6–31G(d) level. The single point energies have been obtained at higher level of G3 (MP2). Four transition states and eight reaction pathways have been revealed and the most favorable reaction to decomposition pathway is the 1, 2‐HCI elimination, which is consistent with the former scientist's conclusion.     

Ab Initio Study of the Excited State Decomposition Reactions of Monothioformic Acid

IntroductionTherehasbeenconsiderableinterestinrecentyearsinthetheoreticalstudyofthemonothioformicacid1ed.However,mostofthemhaveconcentIatedontheelectronicproperties,isomerizationandintramolecularhydrogenshiftreactionsoftheacid,andstudiesonitschemicalreactionshaverarelybeenrepofted.Recently,wereportedonthetheoreticalstudyofthegroundstateunimolecularpyrolysisofmonothioforndcacid,andtheresultsshowedthathightemperatureisneededforitsgroundstatedecompositionreactions.Asapotentialinterstellarcompoun…     

β‐Aminoacrolein: An ab initio,AIM and NBO study

The molecular structure and the intramolecular hydrogen bonding of β‐aminoacrolein and its simple derivatives were investigated at the MP2 and B3LYP levels of theory using the standard 6‐311++G(d, p) basis set. The “atoms in molecules” or AIM theory of Bader which is based on topological properties of the electron density (ρ), was used. Additionally, an analysis of the critical points was performed to study the nature hydrogen bonding in these systems. Natural bond orbital (NBO) analysis was also carried out for to better comprehend the nature of the intramolecular interactions in β‐aminoacrolein and its derivatives. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

配合物[M（CO）3（PPh2py）2]（M=Fe，Ru）异构体的理论研究

对PPh2py配合物[M(CO)3(PPh2py)2](M=Fe,Ru)的三种构型的异构体1-6进行了研究.其中PPh2py以两个P原子与M配位形成HH构型1(Fe)和4(Ru),以一个P和一个N原子与M配位形成HT构型2(Fe)和5(Ru),以两个N原子与M配位形成HH'构型3(Fe)和6(Ru).结果表明,(1)PPh2py中P原子对HOMO轨道的贡献最大,PPh2py作为电子给体时易以P原子与金属原子结合.(2)从分子能量和相互作用能数据表明,配合物中HH构型最稳定,HH'构型最不稳定,这与合成产物为HH构型的结果一致.(3)键长和Wiberg键级均表明P-M键比N-M键结合力强.P、M原子间存在σ键,而N、Fe原子间仅存在nN→nM或nN→σM-P的电荷转移作用.(4)HH构型中M对HOMO的贡献最大,PPh2py向M的电荷转移最强,使M的负电荷最大,故HH构型最易作为电子给体以M原子与第二个金属配位形成双核配合物.     

An Ab Initio Study and NBO Analysis of the Stability and Conformational Properties of Hexakis(trimethylelementhyl)benzene (Element = C,Si, Ge,and Sn)

Ab initio molecular orbital and density functional theory were used to investigate energetic and structural properties of the various conformations of hexa-tertbutylbenzene (1), hexakis(trimethylsilyl)benzene (2), hexakis (trimethylgermyl)benzene (3), and hexakis(trimethylstannyl)benzene (4). HF/3-21G//HF/3-21G and B3LYP/3-21G//HF/3-21G results revealed that the Twist-Boat (TB) conformer of compound 1 is more stable than the 1-Chair (C), 1-Boat (B), and 1-Planar (P) conformers. B3LYP/3-21G//HF/3-21G results show that the 1- TB conformer is more stable than 1- C, 1- B, and 1- P conformers of about 1.13, 4.34, and 99.94 kcal mol^?1 , respectively. Contrary to the stability order of compound 1 conformers, the C conformer of compounds 2–4 is more stable than TB, B, and P conformations, as calculated by B3LYP/3-21G//HF/3-21G and HF/3-21G//HF/3-21G levels of theory. The energy gap between the C and P conformers in compounds 1–4 is decreased in the following order: ΔE(4: C, P) < ΔE (3: C, P) < ΔE(2: C, P) < ΔE (1: C, P). This fact can be explained in terms of the increase of C _aromatic -M (M═C, Si, Ge, and Sn) bond lengths and the decrease of steric (van der Waals) repulsions in the previously discussed compounds. For compounds 1–3, the calculations were also performed at the B3LYP/ 6-31G*//HF/3-21G level of theory. However, the comparison showed that the results at B3LYP/3-21G//HF/3-21G methods correlated well with those obtained at the B3LYP/6-31G*// HF/6-31G method. Further, NBO analysis revealed that in compounds 1–4, the resonance energy associated with the σ_M-C1 to σ*_C2-C3 delocalization is 5.20, 9.68, 11.15, and 12.27 kcal mol^?1, respectively. These resonance energy values could explain the easiness of the ring flipping processes of C, B, and TB conformers of compounds 4 to 1. Also, the NBO results showed that by an increase of the σ_M-C1 → σ *_C2-C3 resonance energies in compounds 1–4, the σ_M-C1 bonding orbital occupancies decrease. This fact could fairly explain the increase of the C_aryl-M bond length from compound 1 to 4. The NBO results are also in good agreement with the calculated energy barriers for the ring flipping of the chair conformations in compounds 1–4, as calculated by B3LYP and HF methods.     

DFT Calculations of the Elimination Kinetics of Silacyclobutanes and its Methyl Derivatives in the Gas-Phase

Abstract

The gas-phase thermal decomposition kinetics of silacyclobutane (1), 1-methyl- silacyclobutane (2), and 1,1-dimethyl-1-silacyclobutane (3) has been theoretically studied at the B3LYP/6-311G**, B3PW91/6-311G**, and MPW1PW91/6-311G** levels. The B3LYP/6-311G** method was found to give a reasonable good agreement with the experimental kinetics and thermodynamic parameters. The decomposition reaction of compounds 1–3 yields ethylene and the corresponding silene. Based on the optimized ground state geometries using B3LYP/6-311G** method, the natural bond orbital (NBO) analysis of donor-acceptor (bonding–antibonding) interactions revealed that the perturbation energies (E₂) associated with the electronic delocalization from σ_Si1–C2 to σ*_C4–Si1 orbitals increase from compounds 1 to 3. The σ_Si1–C2→σ*_C4–Si1 resonance energies for compounds 1–3 are 1.17, 1.26, and 1.43 kcal/mol, respectively. Also, the decomposition process in these compounds is controlled by σ→σ* resonance energies. Moreover, the obtained order of energy barriers could be explained by the number of electron-releasing methyl groups substituted to the Si_sp2 atom. NBO analysis shows that the occupancies of σ_Si1–C2 bonds decrease for compounds 1–3 as 3 < 2 < 1, and the occupancies of σ*_Si1–C2 bonds increase in the opposite order (3 > 2 > 1). Moreover, these results can fairly explain the decrease of the energy barriers (ΔE_o) of the decomposition reaction of compounds 1 to 3. The calculated data demonstrate that in the decomposition process of the studied compounds, the polarization of the C₃–C₄ bond is the rate determining factor. Analysis of bond orders, NBO charges, bond indexes, synchronicity parameters, and IRC calculations indicate that these reactions are occurring through a concerted and asynchronous four-membered cyclic transition state type of mechanism.