Potential energy surface of C6F6− radical anion

Shchegoleva, L. N.; Beregovaya, I. V.; Schastnev, P. V.

doi:10.1016/s0009-2614(99)00944-6

Cited by 35 publications

(36 citation statements)

References 13 publications

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“…However, one could expect [32,33] the stability of a RA toward fragmentation also to increase with growing EA of its neutral precursor. This should also be due to the increase in the C-F bond strength with progressive arene fluorination [25,34,35]. However, the available experimental data [30,36] testify to the opposite tendency.…”

Section: Mechanismmentioning

confidence: 99%

“…This circumstance, together with full absence of similar effects in fragmentation products, causes obviously the intrinsic energy barrier to defy following a reaction free energy and a parallelism of kinetics and thermodynamics to get broken [36]. Nevertheless, a certain correlation exists between these effects in a RA and in its fragmentation TS in the polyfluoroarene series [35,36,38]. This allows estimating in a first approximation the relative RA propensity to fragmentation and predicting its regioselectivity on a DE PS* value and a magnitude of the out-of-plane bending of various C-F bonds in a starting RA, the sites of maximal coincidence of p-and s*-electron densities being most favorable [35][36][37].…”

Section: Mechanismmentioning

confidence: 99%

“…Nevertheless, a certain correlation exists between these effects in a RA and in its fragmentation TS in the polyfluoroarene series [35,36,38]. This allows estimating in a first approximation the relative RA propensity to fragmentation and predicting its regioselectivity on a DE PS* value and a magnitude of the out-of-plane bending of various C-F bonds in a starting RA, the sites of maximal coincidence of p-and s*-electron densities being most favorable [35][36][37]. So, DE PS* values correctly predict an acceleration of RA fragmentation rates with fluorine accumulation in the series of fluorinated benzoates and a preferability of the para fluorine removal (Table 1).…”

Section: Mechanismmentioning

confidence: 99%

See 2 more Smart Citations

Recent advances in practice and theory of polyfluoroarene hydrodehalogenation

Shteingarts

2007

Journal of Fluorine Chemistry

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Section: Mechanismmentioning

confidence: 99%

Section: Mechanismmentioning

confidence: 99%

Section: Mechanismmentioning

confidence: 99%

See 1 more Smart Citation

Recent advances in practice and theory of polyfluoroarene hydrodehalogenation

Shteingarts

2007

Journal of Fluorine Chemistry

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“…20 In fact, the fragmentation process is greatly accelerated by this nonplanarity, because it allows for significant mixing of the π* and the C–F σ* orbitals, effectively lifting the otherwise symmetry forbidden intramolecular electron transfer. Given the importance of both the directionality and shape of the C–F σ* orbital for overlap with the arene π* orbital, it stands to reason that perturbation of either the length or direction of σ* orbitals of the C–F bonds will thus influence the likelihood of the bond’s fragmentation from the radical anion which is formed upon electron addition.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen Bond Directed Photocatalytic Hydrodefluorination: Overcoming Electronic Control

2017

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The photocatalytic C–F functionalization of highly fluorinated arenes is a powerful method for accessing functionalized multifluorinated arenes. The decisive step in the determining regioselectivity in fluorine functionalization is fluoride fragmentation from the radical anion of the multifluorinated arene. To date, the availability of regioisomers has been dictated by the innate electronics of the fluorinated arene, limiting the synthetic utility of the chemistry. This study investigates the remarkable ability of a strategically located hydrogen bond to transcend the normal regioselectivity of the C–F functionalization event. A significant rate acceleration is additionally observed for hydrodefluorination of fluorines that can undergo intramolecular hydrogen bonds that form 5–8 membered cycles with moderately acidic N–Hs. The hydrogen bond is expected to facilitate the fragmentation not only by bending the C–F bond of the radical anion out of planarity, but also by increasing the exothermicity of the fluoride extrusion step through protonation of the naked fluoride. Finally, the synthetic utility of the method is demonstrated in an expedited synthesis of the trifluorinated α-phenyl acetic acid derivative required for the commercial synthesis of Januvia, an anti-diabetic drug. This represents the first synthesis of a commercially important multifluorinated arene via a defluorination strategy, and is significantly shorter than the current strategy.

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“…Figure 3 shows the TR MFE curves: the experi mental curve measured at 273 K and the curve simu lated with the use of the constants given in the figure caption. According to quantum chemical calculation data, the PES of the PFA radical anion is similar to the PES of the hexafluorobenzene radical anion [12]. The replacement of one of the fluorine atoms by an amino group slightly disturbs the Jahn-Teller structure of the surface but does not affect its main feature-pseudor otation with low barriers (≤1.6 kcal/mol).…”

Section: Time Resolved Magnetic Field Effect As a Methods Of Studying mentioning

confidence: 83%

Time-resolved magnetic field effect as a method of studying radical pairs with rapid evolution of spin state

et al. 2015

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103As a rule, organic radical ions in solutions have rather short lifetimes, which makes them unsuitable for study by ESR, and at lifetimes shorter than 10 ns, even by a more sensitive method of optically detected ESR (OD ESR) of spin correlated radical ion pairs [1,2]. At the same time, the method of time resolved mag netic field effect (TR MFE) in recombination fluores cence of such pairs [2, 3] enables the detection of even shorter lived particles. This possibility is determined, first of all, by the time resolution of a setup, which we have managed to improve to ≈1 ns. An additional nec essary condition for identification of such short lived radicals is the existence of hyperfine coupling (HFC) constants in them sufficiently large (≈10 mT) to induce singlet-triplet transitions in the nanosecond time range. It is worth noting that the class of com pounds of interest includes only those with rather short fluorescence times.In this work, the potentialities of the TR MFE method have been demonstrated by the examples of radical anions of two fluoro substituted aromatic compounds-1,2,3,5 tetrafluorobenzene (TFB) and pentafluoroaniline (PFA)-generated by X ray irradi ation of solutions. This method is based on analysis of specific features of the ratio between the kinetic curves of recombination fluorescence in a magnetic field (I B (t) and in the absence of a field (I 0 (t)). In low polar ity solutions, the fluorescence intensity decay caused by recombination of radical ion pairs, in the limit of infinitely short fluorescence time and narrow instru mental function, is given bywhere F(t) is the pair recombination rate, θ is the frac tion of pairs generated in the singlet correlated state, and ρ ss (t) is the population of the singlet stage of such pairs [3]. In this approximation, the ratio(2) referred to as time resolved magnetic field effect, is independent of recombination kinetics F(t). However, at sufficiently high frequencies of ρ ss (t) oscillations caused by large HFC constants, the fluorescence kinetics must be described, not by Eq.(1), but by its integral convolution with the fluorescence probability of excited molecules, which changes exponentially with time, and the Gaussian instrumental function (see, e.g., [4]). Radical ions studied in this work have more than two different HFC constants. Therefore, in simulation of TR MFE curves, the singlet state population ρ ss (t) in strong and zero fields was calculated numerically. The spin relaxation times of the radical ions in the pair were considered in the framework of approximations described elsewhere [3,5].Studies of radical anions by the TR MFE method were carried out in 1-10 mM liquid solutions of TFB and PFA in 2,2,4 trimethylpentane (isooctane). In isooctane, the mobility of excess electrons is very high, and radical anions of electron acceptors form in the subnanosecond time domain. To reduce the contribu tion of the isooctane radical cation (the ESR spectrum width, ≈2 mT) to the spin evolution of the radical pair, a positive charge acceptor-hexameth...

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Potential energy surface of C6F6− radical anion

Cited by 35 publications

References 13 publications

Recent advances in practice and theory of polyfluoroarene hydrodehalogenation

Recent advances in practice and theory of polyfluoroarene hydrodehalogenation

Hydrogen Bond Directed Photocatalytic Hydrodefluorination: Overcoming Electronic Control

Time-resolved magnetic field effect as a method of studying radical pairs with rapid evolution of spin state

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