<sup>31</sup>P CIDNP in the reactions of phosphoranyl radicals

Levin, Ya. A.; Il'yasov, A. V.; Gol'dfarb, E. I.; Vorkunova, E. I.

doi:10.1002/mrc.1270051011

Cited by 7 publications

(2 citation statements)

References 11 publications

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“…In this letter we report definitive steady-state 31 P CIDNP 11,12 evidence for the involvement of T --S intersystem crossing in the triplet RPs [2,3] The radical pair theory of CIDNP 13 predicts that under conditions of T 0 -S mixing the net polarization (Γ net , emission or absorption) of a product is dependent upon four parameters (eq 8): the initial spin multiplicity of the radical pair (µ), the mode of product formation ( , in-cage or escape), the sign of the difference in g factors of the two radicals (∆g), and the sign of the hfcc (a) of the nucleus whose polarization is observed. Thus the sign of the polarization will depend on whether product formation from a given polarized radical occurs before or after it exits the initial solvent cage.…”

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confidence: 65%

“…In this letter we report definitive steady-state 31 P CIDNP , evidence for the involvement of T - −S intersystem crossing in the triplet RPs [ 2 , 3 ] generated from photolysis of 1 in benzene solution at ambient temperature. The key observation is the magnetic field strength dependence of the net polarization of product 10 formed on trapping of cage-free phosphonyl radical 3 by benzyl bromide (eq 7) and other radical scavengers which switched from absorption at 58.8 kG (T 0 −S) to emission at 18.8 kG (T - −S).…”

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confidence: 99%

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Magnetic Field Dependence of the ³¹P CIDNP in the Photolysis of a Benzyl Phosphite. Evidence for a T_-−S Mechanism

Koptyug¹,

Sluggett²,

Ghatlia³

et al. 1996

J. Phys. Chem.

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31 P chemically induced dynamic nuclear polarization (CIDNP) studies of the photochemistry of p-acetylbenzyl dimethyl phosphite (1) provide evidence for the operation of the relatively rare T --S intersystem crossing mechanism for a photochemically generated triplet free radical pair. The mechanism of intersystem crossing of the triplet radical pair p-acetylbenzyl (2) and dimethoxyphosphonyl (3), generated from 1, is influenced by the large 31 P hfcc of 3 and switches from the T --S mechanism in a relatively low magnetic field (18.8 kG) to the conventional T 0 -S pathway at a higher field (58.8 kG). This change in mechanism is evidenced by the photolysis of 1 in the presence of radical scavengers (halocarbons, thiophenol) which yields the corresponding products from atom abstraction by 3 that has escaped the initial radical cage. These escape products are absorptiVely polarized at high field (T 0 -S) but are emissiVely polarized at lower field (T --S) in a particularly well-defined display of the effect of magnetic field strength on intersystem crossing mechanism for a geminate radical pair. Photolysis of 1 in C 6 D 6 solution yields emissively polarized dimethyl p-acetylbenzylphosphonate (4) from combination of radical pair [2,3] in the initial solvent cage and following diffusive formation of [2,3] free pairs. Cage recombination and disproportionation of secondary F pairs, comprised of 2 and the phosphorus-substituted cyclohexadienyl radical (5), affords several emissively polarized products (6, 7, and 9) via the T 0 -S mechanism at both magnetic fields. The polarization of 4 remains emissive at both magnetic fields regardless of the presence of radical scavengers, a finding which is argued to be consistent with the above results.Several mechanisms can be operative in the generation of both chemically induced dynamic electron (CIDEP) and nuclear polarization (CIDNP) observed in the ESR spectra of radical intermediates and in the NMR spectra of radical-derived products, respectively. 1-3 For radical pairs (RP) in solution, the most commonly encountered mechanism responsible for both phenomena is the T 0 -S mixing of spin states. Much more rarely the T --S mechanism prevails, and usually requires the mobility of the partners in the pair to be restricted, e.g., as in highly viscous solvents 4 or in biradicals. 5 However, the T --S mechanism can be operative for a RP in solution at ambient temperature 6,7 if one of the radicals possesses an unusually large hyperfine coupling constant (hfcc). Time-resolved ESR studies 8 have implicated the possible involvement of T --S transitions in CIDEP phenomena observed on generation of the triplet primary RP [2,3] by photolysis of p-acetylbenzyl dimethyl phosphite (1) in solution in a 3.5 kG magnetic field (eq 1, Scheme 1). Indeed, the hfcc of phosphonyl radical 3 is large (ap ≈ 700 G) [8][9][10] and could facilitate intersystem crossing by the T --S pathway. However, a unique interpretation of the CIDEP data could not be made due to the simultaneous action of several elect...

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confidence: 65%

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confidence: 99%

Magnetic Field Dependence of the ³¹P CIDNP in the Photolysis of a Benzyl Phosphite. Evidence for a T_-−S Mechanism

Koptyug¹,

Sluggett²,

Ghatlia³

et al. 1996

J. Phys. Chem.

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Reaktionen trivalenter Phosphorverbindungen mit tert‐Butoxylradikalen

Schwetlick

Pionteck

König³

et al. 1986

Zeitschrift fuer Chemie

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The products of the reaction of several alkyl, aryl, sterically hindered aryl and cyclic phosphites, thiophosphites, benzenephosphonites and triphenylphosphine with tert‐butoxyl radicals generated by thermolysis of di‐tert‐butyl peroxalate (DTBPO) in chlorobenzene at 50°C was studied. Alkyl phosphites are oxidized to the corresponding phosphates by β‐scission of the intermediate phosphoranyl radicals. Phenyl phosphites react under displacement of a phenoxyl to give tert‐butyl phosphites by α‐scission of the intermediate phosphoranyl radicals. Sterically hindered p‐methyl‐phenyl phosphites also form the tert‐butyl phosphites accompanied by rearranged p‐hydroxyphenylmethanephosphonates. Cyclic arylene phosphites are predominantly oxidized, substitution takes place to a minor extent. Benzenephosphonites and phosphines react with tert‐butoxyl radicals by oxidation to give the corresponding phosphonates and phosphine oxide, resp. Those phosphorus compounds which are oxidized with the formation of tert‐butyl radicals accelerate the thermal decomposition of DT BPO under the condition studied.

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Phosphoranyl Radicals

Bentrude¹

1983

Reactive Intermediates

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³¹P CIDNP in the reactions of phosphoranyl radicals

Abstract: Abstract-The polarisation of phosphorus nuclei CIP CIDNP) during the free radical reactions of trialkyl and triaryl phosphites proceeding via intermediate phosphoranyl radicals is discussed.

Cited by 7 publications

References 11 publications

Magnetic Field Dependence of the ³¹P CIDNP in the Photolysis of a Benzyl Phosphite. Evidence for a T_-−S Mechanism

Magnetic Field Dependence of the ³¹P CIDNP in the Photolysis of a Benzyl Phosphite. Evidence for a T_-−S Mechanism

Reaktionen trivalenter Phosphorverbindungen mit tert‐Butoxylradikalen

Phosphoranyl Radicals

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31P CIDNP in the reactions of phosphoranyl radicals

Abstract: Abstract-The polarisation of phosphorus nuclei CIP CIDNP) during the free radical reactions of trialkyl and triaryl phosphites proceeding via intermediate phosphoranyl radicals is discussed.

Cited by 7 publications

References 11 publications

Magnetic Field Dependence of the 31P CIDNP in the Photolysis of a Benzyl Phosphite. Evidence for a T-−S Mechanism

Magnetic Field Dependence of the 31P CIDNP in the Photolysis of a Benzyl Phosphite. Evidence for a T-−S Mechanism

Reaktionen trivalenter Phosphorverbindungen mit tert‐Butoxylradikalen

Phosphoranyl Radicals

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³¹P CIDNP in the reactions of phosphoranyl radicals

Magnetic Field Dependence of the ³¹P CIDNP in the Photolysis of a Benzyl Phosphite. Evidence for a T_-−S Mechanism

Magnetic Field Dependence of the ³¹P CIDNP in the Photolysis of a Benzyl Phosphite. Evidence for a T_-−S Mechanism