Singlet Reaction Research Articles

Quantitative measurements of reactive oxygen species partitioning in electron transfer flavoenzyme magnetic field sensing.

Biological magnetic field sensing that gives rise to physiological responses is of considerable importance in quantum biology. The radical pair mechanism (RPM) is a fundamental quantum process that can explain some of the observed biological magnetic effects. In magnetically sensitive radical pair (RP) reactions, coherent spin dynamics between singlet and triplet pairs are modulated by weak magnetic fields. The resulting singlet and triplet reaction products lead to distinct biological signaling channels and cellular outcomes. A prevalent RP in biology is between flavin semiquinone and superoxide (O2 •-) in the biological activation of molecular oxygen. This RP can result in a partitioning of reactive oxygen species (ROS) products to form either O2 •- or hydrogen peroxide (H2O2). Here, we examine magnetic sensing of recombinant human electron transfer flavoenzyme (ETF) reoxidation by selectively measuring O2 •- and H2O2 product distributions. ROS partitioning was observed between two static magnetic fields at 20nT and 50μT, with a 13% decrease in H2O2 singlet products and a 10% increase in O2 •- triplet products relative to 50µT. RPM product yields were calculated for a realistic flavin/superoxide RP across the range of static magnetic fields, in agreement with experimental results. For a triplet born RP, the RPM also predicts about three times more O2 •- than H2O2, with experimental results exhibiting about four time more O2 •- produced by ETF. The method presented here illustrates the potential of a novel magnetic flavoprotein biological sensor that is directly linked to mitochondria bioenergetics and can be used as a target to study cell physiology.

Theoretical Exploration of Energy Transfer and Single Electron Transfer Mechanisms to Understand the Generation of Triplet Nitrene and the C(sp3)-H Amidation with Photocatalysts.

Mechanistic explorations and kinetic evaluations were performed based on electronic structure calculations at the CASPT2//CASSCF level of theory, the Fermi's golden rule combined with the Dexter model, and the Marcus theory to unveil the key factors regulating the processes of photocatalytic C(sp3)-H amidation starting from the newly emerged nitrene precursor of hydroxamates. The highly reactive nitrene was found to be generated efficiently via a triplet-triplet energy transfer process and to be benefited from the advantages of hydroxamates with long-range charge-transfer (CT) excitation from the N-centered lone pair to the 3,5-bis(trifluoromethyl)benzoyl group. The properties of the metal-to-ligand charge-transfer (MLCT) state of photocatalysts, the functionalization of chemical moieties for substrates involved in the charge-transfer (CT) excitation, such as the electron-withdrawing trifluoromethyl group, and the energetic levels of singlet and triplet reaction pathways may regulate the reaction yield of C(sp3)-H amidation. Kinetic evaluations show that the triplet-triplet energy transfer is the main driving force of the reaction rather than the single electron transfer process. The effects of electronic coupling, molecular rigidity, and excitation energies on the energy transfer efficiency were further discussed. Finally, we investigated the inverted behavior of single-electron transfer, which is correlated unfavorably to the catalytic efficiency and amidation reaction. All theoretical explorations allow us to better understand the generation of nitrene with visible-light photocatalysts, to expand highly efficient substrate sources, and to broaden our scope of available photosensitizers for various cross-coupling reactions and the construction of N-heterocycles.

Tuning Deazaflavins Towards Highly Potent Reducing Photocatalysts Guided by Mechanistic Understanding - Enhancement of the Key Step by the Internal Heavy Atom Effect.

Deazaflavins are well suited for reductive chemistry acting via a consecutive photo‐induced electron transfer, in which their triplet state and semiquinone – the latter is formed from the former after electron transfer from a sacrificial electron donor – are key intermediates. Guided by mechanistic investigations aiming to increase intersystem crossing by the internal heavy atom effect and optimising the concentration conditions to avoid unproductive excited singlet reactions, we synthesised 5‐aryldeazaflavins with Br or Cl substituents on different structural positions via a three‐component reaction. Bromination of the deazaisoalloxazine core leads to almost 100 % triplet yield but causes photo‐instability and enhances unproductive side reactions. Bromine on the 5‐phenyl group in ortho position does not affect the photostability, increases the triplet yield, and allows its efficient usage in the photocatalytic dehalogenation of bromo‐ and chloroarenes with electron‐donating methoxy and alkyl groups even under aerobic conditions. Reductive powers comparable to lithium are achieved.

Excited state modulation of C70 dimerization in a carbon nanotube under a variable electron acceleration voltage

Cinematographic recording of chemical reactions with transmission electron microscopy provides information unavailable by any other analytical methods. Studies have thus far remained mostly phenomenological, lacking information on the reactive species involved. To gain insight into the nature of the reactive species, we need to obtain kinetic information under various temperatures and variable acceleration voltages, i.e., electronic energy supply. We studied the mechanism of [2 + 2] dimerization of [70] fullerene in a carbon nanotube as an example. We describe herein a statistical analysis of individual reaction events of the dimerization that revealed dose-dependent first-order kinetics and voltage-dependent crossover from a singlet to a triplet mechanism, as highlighted by the pre-exponential factor (the frequency of excitation) that is a million times larger for the singlet reaction than for the triplet one. Comparison with the results of a recent study of [60] fullerene dimerization lets us propose that electron-impact excitation of the carbon nanotube is the first step, followed by energy transfer to fullerene molecules and their dimerization via an excited state. The results show that a variable-voltage kinetic study is indispensable for discussing the mechanism of chemical transformations under electron microscopic observation.

A DFT study on the reaction mechanisms of the oxidation of ethylene mediated by technetium and manganese oxo complexes.

The oxidation of ethylene catalyzed by manganese and technetium oxo complexes of the type MO3L (M = Tc, Mn, and L = O-, Cl-, F-, OH-, Br-, I-) on both singlet and triplet potential energy surfaces (PESs) have been studied. All molecular structures were stable on the singlet PES except for the formation of the dioxylate intermediate for the MnO3L (L = O-, Cl-, F-, OH-, Br-, I-) catalyzed pathway. Frontier molecular orbital calculations showed that electrons flow from the HOMO of ethylene into the LUMO of the metal-oxo complex for all complexes studied except for MO3L (M = Tc, Mn, and L = O-) where the vice versa occurs. In the reaction of both TcO3L and MnO3L (L = O-, Cl-, F-, OH-, Br-, I-) with ethylene, it was observed that the formation of the dioxylate intermediate along the [3 + 2] addition pathway on the singlet reaction surface is both kinetically and thermodynamically favorable over its formation via the [2 + 2] pathway. Furthermore, it was observed that TcO4- and MnO4- catalyzed pathways exclusively form diols on the singlet PES. The formation of epoxides on the singlet surface is kinetically favorable through the [2 + 1] and [2 + 2] channel for the MnO3L (L = F-, Cl-, Br-, I-, OH-) and TcO3L (L = F-, Cl-, Br-, I-, OH-) catalyzed surfaces respectively. In all cases, the TcO3L complexes were found to be polar compared to the MnO3L complexes. The MnO4- (singlet) and MnO3F (singlet) are the best catalysts for the exclusive formation of the diols and epoxides respectively.

Theoretical study on the reduction reactions from solid char(N): The effect of the nearby group and the high-spin state

A fundamental understanding of the reduction reactions from solid char(N) is proposed with the aim of providing useful information to aid in minimising NOx emission. The direct reduction with (a) nearby radical; (b) nearby oxygen and (c) nearby vacancy is calculated. The results show that the nearby oxygen will increase the activation energy by 51.8 kJ/mol and the nearby vacancy will reduce the exothermicity by 269.7 kJ/mol. This leads us to the firm conclusion that the nearby radical site will provide a favorable route. The indirect reduction reactions from surface migration are also determined. According to the calculated results, the high-spin singlet reactions are more complicated than the low-spin triplet reactions. The barrier height involved in the singlet reactions is much lower than that encountered in the triplet reactions, indicating that the reaction with singlets holds potential of being an important channel for N2 production. Our qualitative analysis of the density functional theory (DFT) results confirms that the high-spin excited-state changing the electronic properties of the carbonaceous surface is much more favorable for the reduction than the low-spin ground-state. Much more emphasis therefore should be placed on the high-spin states during the mechanism study of the heterogeneous reactions.

Theoretical studies on the mechanism and kinetic for CH3CH2O + HO2 and CH3CHOH + HO2 reactions

AbstractThe singlet and triplet reaction mechanisms and rate constants for CH3CH2O + HO2 and CH3CHOH + HO2 reactions were investigated by employing the high‐level quantum chemical calculations with CBS‐QB3 theoretical method and conventional transition state theory with the Wigner tunneling correction. For CH3CH2O + HO2 reaction, four direct hydrogen abstraction processes and five addition‐elimination channels were identified, while two direct hydrogen abstraction routes and nine addition‐elimination channels were found in CH3CHOH + HO2 reaction. The results show that the triplet addition‐elimination channels of CH3CH2OH + 3O2 and CH3COOH + H2O are, respectively, the most favorable channels for CH3CH2O + HO2 and CH3CHOH + HO2 reactions. This is because that they have lower energy barrier and their contribution to the overall rate constants are, respectively, 57% to 86% and 44% to 80%. This work may lead to a better understanding of the mechanism and the kinetic for the singlet and triplet reactions of CH3CH2O + HO2 and CH3CHOH + HO2.

Mechanistic and kinetic study on the reaction of Pyrrole (C4H5N) with O(3P)

The mechanism and kinetic for the reaction of Pyrrole + O(3P) has been investigated using CCSD(T)//M06-2X method with multichannel RRKM-TST calculation. On the triplet surface, four product channels corresponding to α-C-addition, β-C-addition, N-addition and direct H-abstraction have been characterized for the first time. The rate constants and branching ratios for twelve product channels are calculated. It is predicted that the total rate coefficients vary with temperature, and exhibit strong positive temperature dependence. Moreover, the total rate coefficients are independence pressure. On the singlet surface, the atomic oxygen can easily add to the CC double bond or the N atom of Pyrrole forming intermediate s-IM1or s-IM2; both approaches were found to be barrierless. It is indicated that the singlet reaction exhibits a marked difference from the triplet reaction. This calculation is useful to simulate experimental investigations of the Pyrrole + O reaction in the singlet surface.

Reactions of aldehyde with collagen: a DFT study

The reaction mechanisms of several amino acids (Asn, Gln, Arg, His, and Lys) in the collagen with aldehyde were studied using density functional theory method. Based on the geometry optimization, results expounded the singlet and doublet reaction mechanisms, respectively, and discussed the structural properties of intermediates, transition states, and products that appeared along the corresponding potential energy surfaces. The reaction along the doublet potential energy surface is more thermodynamically favorable than that along the singlet one. However, the reactions obeying the doublet route only produce the carbinolamine type of compounds, rather than the Schiff bases. It is because that the doublet mechanism involves only the hydrogen abstraction or hydrogen exchange process, without the dehydration process. The Schiff base types of compounds are most likely to be obtained from the singlet reactions of Asn, Gln, Arg, and Lys with aldehyde. In order to assist the experiment in identification of product structures and reaction mechanism correctly, the vibrational modes of each product with distinctive features were analyzed and compared in detail.

An ab Initio Exploration of the Bergman Cyclization.

The Bergman cyclization is an important reaction in which an enediyne cyclizes to produce a highly reactive diradical species, p-benzyne. Enediyne motifs are found in natural antitumor antibiotic compounds, such as calicheammicin and dynemicin. Understanding the energetics of cyclization is required to better control the initiation of the cyclization, which induces cell death. We computed the singlet and triplet potential energy surfaces for the Bergman cyclization of (Z)-hex-3-ene-1,5-diyne using the CCSD and EOM-SF-CCSD methods. The triplet enediyne and transition state were found to have C2 symmetry, which contrasts with the singlet reactant and transition state that possess C2v symmetry. We analyzed the frontier orbitals of both cyclization pathways to explain the large energetic barrier of the triplet cyclization. Reaction energies were calculated using CCSD(T)/cc-pVTZ single-point calculations on structures optimized with CCSD/cc-pVDZ. The singlet reaction was found to be slightly endothermic (ΔHrxn = 13.76 kcal/mol) and the triplet reaction was found to be highly exothermic (ΔHrxn = -33.29 kcal/mol). The adiabatic singlet-triplet gap of p-benzyne, computed with EOM-SF-CCSD/cc-pVTZ, was found to be 3.56 kcal/mol, indicating a singlet ground state.

Gas phase Boudouard reactions involving singlet–singlet and singlet–triplet CO vibrationally excited states: implications for the non-equilibrium vibrational kinetics of CO/CO2 plasmas

Rate constants for the Boudouard reactions: CO + CO → CO2 + C and CO + CO → C2O + O, involving ground and vibrationally excited states for both singlet–singlet and singlet–triplet reactant CO molecules, have been obtained by using the transition-state theory on an ab initio generated potential energy surface. The dependence of the activation energies for the different processes on the vibrational energy of reactants has been estimated through a parametrization that accounts for the utilization of vibrational energy and is calculated by the forward and backward ab initio activation energies of the relevant processes at zero vibrational energy. The results and their comparison with available experimental reaction rates demonstrate the importance of vibrational excitation not only for the singlet–singlet reactions, but also for the singlet–triplet ones, which are here investigated for the first time. Finally, the implications of the present results on the kinetics of CO/CO2 cold plasmas are discussed: for their modeling the temperature dependence of the obtained rates for singlet–singlet and singlet–triplet reactants in the ground vibrational states have been represented by both Arrhenius and deformed Arrhenius equations.

A meta-analysis and review examining a possible role for oxidative stress and singlet oxygen in diverse diseases.

From kinetic data (k, T) we calculated the thermodynamic parameters for various processes (nucleation, elongation, fibrillization, etc.) of proteinaceous diseases that are related to the β-amyloid protein (Alzheimer's), to tau protein (Alzheimer's, Pick's), to α-synuclein (Parkinson's), prion, amylin (type II diabetes), and to α-crystallin (cataract). Our calculations led to ΔG≠ values that vary in the range 92.8-127 kJ mol-1 at 310 K. A value of ∼10-30 kJ mol-1 is the activation energy for the diffusion of reactants, depending on the reaction and the medium. The energy needed for the excitation of O2 from the ground to the first excited state (1Δg, singlet oxygen) is equal to 92 kJ mol-1 So, the ΔG≠ is equal to the energy needed for the excitation of ground state oxygen to the singlet oxygen (1Δg first excited) state. The similarity of the ΔG≠ values is an indication that a common mechanism in the above disorders may be taking place. We attribute this common mechanism to the (same) role of the oxidative stress and specifically of singlet oxygen, (1Δg), to the above-mentioned processes: excitation of ground state oxygen to the singlet oxygen, 1Δg, state (92 kJ mol-1), and reaction of the empty π* orbital with high electron density regions of biomolecules (∼10-30 kJ mol-1 for their diffusion). The ΔG≠ for cases of heat-induced cell killing (cancer) lie also in the above range at 310 K. The present paper is a review and meta-analysis of literature data referring to neurodegenerative and other disorders.

Oxidation of Methane to Methanol over Single Site Palladium Oxide Species on Silica: A Mechanistic view from DFT

A theoretical analysis was carried out on the mechanism of methane oxidation to methanol occurring on single site palladium oxide species [PdO]2+ supported on a model of Al-MCM-41 silica. Both 6- and 8-membered ring structures were considered to represent the support. The energy profile for each elementary reaction was determined from density functional theory calculations with the OPBE functional. The calculated overall activation energies are close to the experimental values. Our calculations confirm that spin inversion can play a significant role in decreasing the barrier heights for the pathways. Indeed, in this type of reactions we could show a crossing between singlet and triplet reaction paths. We showed that the mechanism for the C-H bond cleavage and for the formation of methanol has a radical nature. According to our results, the [PdO]2+ species located on a 8-membered ring of silica is more active than that deposited on a 6-membered ring. The calculated activation energies to cleave the methane C-H bond are 35 and 84 kJ/mol for the radical and ionic pathways, respectively. The activation barrier and the transition state geometry of this H-abstraction step are directly correlated with the optimal angle at which the substrate should approach the [Pd═O]2+ moiety, with the elongation of the Pd-Ooxo bond and finally with the energy of the π* acceptor orbital.

Singlet versus Triplet Excited State Mediated Photoinduced Dehalogenation Reactions of Itraconazole in Acetonitrile and Aqueous Solutions.

Photoinduced dehalogenation of the antifungal drug itraconazole (ITR) in acetonitrile (ACN) and ACN/water mixed solutions was investigated using femtosecond and nanosecond time-resolved transient absorption (fs-TA and ns-TA, respectively) and nanosecond time-resolved resonance Raman spectroscopy (ns-TR3) experiments. An excited resonance energy transfer is found to take place from the 4-phenyl-4,5-dihydro-3H-1,2,4-triazol-3-one part of the molecule to the 1,3-dichlorobenzene part of the molecule when ITR is excited by ultraviolet light. This photoexcitation is followed by a fast carbon-halogen bond cleavage that leads to the generation of radical intermediates via either triplet and/or singlet excited states. It is found that the singlet excited state-mediated carbon-halogen cleavage is the predominant dehalogenation process in ACN solvent, whereas a triplet state-mediated carbon-halogen cleavage prefers to occur in the ACN/water mixed solutions. The singlet-to-triplet energy gap is decreased in the ACN/water mixed solvents and this helps facilitate an intersystem crossing process, and thus, the carbon-halogen bond cleavage happens mostly through an excited triplet state in the aqueous solutions examined. The ns-TA and ns-TR3 results also provide some evidence that radical intermediates are generated through a homolytic carbon-halogen bond cleavage via predominantly the singlet excited state pathway in ACN but via mainly the triplet state pathway in the aqueous solutions. In strong acidic solutions, protonation at the oxygen and/or nitrogen atoms of the 1,2,4-triazole-3-one group appears to hinder the dehalogenation reactions. This may offer the possibility that the phototoxicity of ITR due to the generation of aryl or halogen radicals can be reduced by protonation of certain moieties in suitably designed ITR halogen-containing derivatives.

Singlet oxygen generation from poly[4-diacetoxyiodo]styrene and hydrogen peroxide

Treatment of hydrogen peroxide with a polymer-supported hypervalent iodine compound, poly[4-diacetoxyiodo] styrene (PDAIS), generates singlet molecular oxygen ($^{1}$O$_{2})$. Singlet oxygen generation was proved by trapping with typical organic compounds such as conjugated dienes, aromatic dienes, and electron-rich alkene. When compared to monomer analogue, the use of PDAIS in peroxidation of substrates gave slightly better yields (45%-96%). Regeneration and reuse of PDAIS showed similar activity. The mechanism underlying generation of singlet oxygen and reaction scope was examined.

Reaction of NO3 radical with benzyl alcohol - A DFT study

Volatile primary aromatic benzyl alcohol (BzOH) reacts with strong atmospheric oxidants like OH, Cl, NO3 radicals. The present study elucidates detailed investigation of gas phase reaction mechanisms of benzyl alcohol with NO3 radicals using density functional theory at M06-2X/6-311+G(d,p) and MPW1K/6-311+G(d,p) levels. The results show that the H-abstraction from methyl group is more energetically favorable with small barrier height. Single-point energy calculations were also performed at the CCSD(T)/6-311+G(d,p) level of theory. The spin state analysis (singlet, triplet) concludes ground state (singlet) reactions are feasible. The reaction force profile along the reaction path is rationalized in terms of structural and electronic rearrangements that take place during the chemical transformation. From the reaction force analysis, it is evident that structural rearrangement plays more dominant role than electronic reordering in this reaction. The calculated rate constant of H-atom abstraction from methyl group of benzyl alcohol with NO3 radical is 16.72×10−15cm3molecule−1s−1, which is in good agreement with experimental study. Overall, NO3 will replace OH and play a major role in reaction with BzOH during night time.

The Driving Force of Photoinduced Charge Separation in Metal-Cluster-Encapsulated Triphenylamine-[80]fullerenes.

Understanding photoinduced charge separation in fullerene-based dye-sensitized solar cells is crucial for the development of photovoltaic devices. We investigate here how the driving force of the charge separation process in conjugates of M@C80 (M=Sc3 N, Sc3 CH, Sc3 NC, Sc4 O2 , and Sc4 O3 ) with triphenylamine (TPA) depends on the nature of the metal cluster. Both singlet and triplet excited-state electron-transfer reactions are considered. These results based on TD-DFT calculations demonstrate that the driving force of charge separation in TPA-M@C80 can be tuned well by varying the structure of the metal cluster encapsulated inside the fullerene cage.

Reaction Mechanism of 3,4-Dinitrofuroxan Formation from Glyoxime: Dehydrogenation and Cyclization of Oxime.

The reaction pathway of the formation of 3,4-dinitrofuroxan from glyoxime is theoretically investigated under experimental conditions with 25 % nitric acid and dinitrogentetroxide reagents to clarify the mechanism of formation of a furoxan ring by glyoxime. The geometric configurations of minima and transition-state species are optimized at the (U)B3LYP/6-311++G** level. The CCSD(T) and CASSCF(10e,8o)/CASSCF(9e,8o) single-point energy corrections at the same level are performed on top of the optimized geometries. A subsequent dynamic correlation by using NEVPT2/6-311++G**-level single-point energy calculations based on the CASSCF results is also performed to obtain accurate energy values. The formation reaction is analyzed from two processes: glyoxime nitration and 3,4-dinitroglyoxime (nitration product) oxidative cyclization. Calculation results indicate that the electrophilic substitution of nitronium ions from the protonated HNO3 and the abstraction of hydrogen ions by HNO3 molecules are requisites of glyoxime nitration. The formation of a furoxan ring from 3,4-dinitroglyoxime involves two possible mechanisms: 1) oxydehydrogenation by NO2 molecules and the subsequent torsion of NO radical groups to form a ring and 2) the alternation of dehydrogenation and cyclization. The intermediates and transition states in both routes exhibit monoradical and diradical characteristics. Singlet and triplet reactions are considered for the diradical species. Results show that the singlet reaction mechanism is more favorable for cyclization than the triplet reaction. The formation of a furoxan ring from oxime is in accordance with the stepwise intermolecular dehydrogenation and intramolecular torsion to the ring.

Mechanistic investigation of dirhodium-catalyzed intramolecular allylic C-H amination versus alkene aziridination.

The reaction mechanisms and chemoselectivity on the intramolecular allylic C-H amination versus alkene aziridination of 4-pentenylsulfamate promoted by four elaborately selected dirhodium paddlewheel complexes are investigated by a DFT approach. A predominant singlet concerted, highly asynchronous pathway and an alternative triplet stepwise pathway are obtained in either C-H amination or alkene aziridination reactions when mediated by weak electron-donating catalysts. A singlet stepwise C-H amination pathway is obtained under strongly donating catalysts. The rate-determining step in the C-H amination is the H-abstraction process. The subsequent diradical-rebound C-N formation in the triplet pathway or the combination of the allylic carbocation and the negative changed N center in the singlet pathway require an identical energy barrier. A mixed singlet-triplet pathway is preferred in either the C-H insertion or alkene aziridination in the Rh2(NCH3CHO)4 entry that the triplet pathway is initially favorable in the rate-determining steps, and the resultant triplet intermediates would convert to a singlet reaction coordinate. The nature of C-H amination or alkene aziridination is estimated to be a stepwise process. The theoretical observations presented in the paper are consistent with the experimental results and, more importantly, provide a thorough understanding of the nature of the reaction mechanisms and the minimum-energy crossing points.

Computational study of singlet and triplet sulfonylnitrenes insertion into the C―C or C―H bonds of ethylene

Formation of N-sulfonylaziridines, N-ethylidenesulfonamides, N-vinylsulfonamides and 4,5-dihydro-1,2,3-oxathiazole 2-oxides by the reaction of singlet and triplet trifluoromethyl-, methyl- and tosylnitrenes with ethylene is studied computationally at the B3LYP/6-311++G(d,p) level of theory in both gas phase and in solution. Singlet sulfonylnitrenes react with ethylene via [1 + 2]-cycloaddition exothermically to give N-sulfonylaziridines. Triplet sulfonylnitrenes are formed from the singlet ones by the intersystem crossing with the energy barrier not exceeding 2.5 kcal/mol and react in a stepwise fashion by C-addition or H-abstraction. The C-addition gives rise to the formation of N-sulfonylaziridines or N-ethylidenesulfonamides depending on the S―N―Csp3―Csp2 dihedral angle, with the barrier to rotation about the N―Csp3 bond not exceeding 2.5 kcal/mol. The H-abstraction results in N-vinylsulfonamides. Transformation of N-sulfonylaziridines to N-ethylidenesulfonamides requires to overcome the barrier of 57–60 kcal/mol, N-ethylidenesulfonamides to 4,5-dihydro-1,2,3-oxathiazole 2-oxides—74–80 kcal/mol and N-vinylsulfonamides to N-ethylidenesulfonamides—about 64 kcal/mol. The use of the polarizable continuum model does not lead to a change of the course of the reaction of trifluoromethanesulfonylnitrene with ethylene and only slightly affects the relative energies of the products, intermediates and transition states. Copyright © 2014 John Wiley & Sons, Ltd.