Spectral and kinetic measurements on a series of persistent iminoxyl radicals

Eisenhauer, Brian M.; Wang, Minghui; Brown, R. W.; Labaziewicz, Henryk; Ngo, Maria; Kettinger, Karl W.; Mendenhall, G. D.

doi:10.1002/(sici)1099-1395(199710)10:10<737::aid-poc944>3.0.co;2-n

Cited by 10 publications

(11 citation statements)

References 27 publications

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“…The following sterically-protected iminoxyls have been isolated as blue liquids: Me 3 C(EtCMe 2 )C=NO • , (EtCMe 2 ) 2 C=NO • , and Me 3 C(Et 3 C)C=NO • . 20 Although they are more sterically congested than (Me 3 C) 2 C=NO • , the second order rate constants (2k 13 ) for the decay of two of them, Me 3 C(EtCMe 2 )C=NO • and (EtCMe 2 ) 2 C=NO • , are about three times as great as 2k 13 for di-tert-butyliminoxyl 23 (Table 6.1). Only Me 3 C(Et 3 C)C=NO • decayed at a slightly lower rate than (Me 3 C) 2 C=NO • (Table 6.1).…”

Section: Di-tert-alkyliminoxyls More Sterically Crowded Than Di-tert-mentioning

confidence: 93%

“…The reactions of di-tert-butyliminoxyl with alkenes are much faster than with alkyl aromatic hydrocarbons, for example, 23 10 5 × k obs /M −1 s −1 = 2.0, 3.3, 4.0, and 5.1, at 28 • C for 2-methylpent-2-ene, 2,3-dimethylbut-2-ene, cyclohexene, and cyclopentadiene, respectively. These reactions are complete in about 90 minutes at room temperature.…”

Section: Oxidation Of Hydrocarbons With Di-tert-butyliminoxylmentioning

confidence: 99%

“…23 These reactions have a large deuterium kinetic isotope effect, for example, replacement of the tertiary (benzylic) hydrogen atom in isopropylbenzene by a deuterium atom yielded: k H 15 /k D 15 = 14.4 (±1.8) at 120 • C. 19 The temperature dependence of hydrogen atom abstraction from isopropylbenzene can be described by Equation 6.17 19 :…”

Section: Oxidation Of Hydrocarbons With Di-tert-butyliminoxylmentioning

confidence: 99%

“…However, the kinetics of decay of this iminoxyl did not correspond to a simple second order process and gave between 9 and 11 products (HPLC) with traces of pivalonitrile and triethylacetonitrile, but no detectable (<1 %) 4,4-diethyl-2,2-dimethylhexan-3-one. 23 In contrast, the decay of (Me 3 C) 2 C=NO • gave 4 % pivalonitrile and 40 % di-tert-butyl ketone (vide supra). 19 At high concentrations of Me 3 C(Et 3 C)C=NO • (0.2 M) decay followed reasonable first order kinetics (k obs = 2.3 × 10 −5 s −1 in acetonitrile at 23 • C), probably via an intramolecular hydrogen atom abstraction (Equations 6.27 and 6.…”

Section: Di-tert-alkyliminoxyls More Sterically Crowded Than Di-tert-mentioning

confidence: 99%

See 3 more Smart Citations

The Only Stable Organic Sigma Radicals: Di‐ tert ‐Alkyliminoxyls

Ingold

2010

Stable Radicals

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Section: Di-tert-alkyliminoxyls More Sterically Crowded Than Di-tert-mentioning

confidence: 93%

Section: Oxidation Of Hydrocarbons With Di-tert-butyliminoxylmentioning

confidence: 99%

Section: Oxidation Of Hydrocarbons With Di-tert-butyliminoxylmentioning

confidence: 99%

Section: Di-tert-alkyliminoxyls More Sterically Crowded Than Di-tert-mentioning

confidence: 99%

See 2 more Smart Citations

The Only Stable Organic Sigma Radicals: Di‐ tert ‐Alkyliminoxyls

Ingold

2010

Stable Radicals

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“…Attempts to increase the stability of the iminoxyl radical by replacing the tert-butyl substituent with a bulkier triethylmethyl or other acyclic tert-alkyl substituents were not successful. In the case of Me 3 C(Et 3 C)C=NO • radical 14, a monomolecular decomposition process was proposed, associated with an intramolecular hydrogen atom abstraction by an iminoxyl radical leading to the intermediate 15 (Scheme 4) [35,60,61].…”

Section: Reviewmentioning

confidence: 99%

Oxime radicals: generation, properties and application in organic synthesis

Krylov¹,

Paveliev²,

Budnikov³

et al. 2020

Beilstein J. Org. Chem.

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N-Oxyl radicals (compounds with an N–O• fragment) represent one of the richest families of stable and persistent organic radicals with applications ranging from catalysis of selective oxidation processes and mechanistic studies to production of polymers, energy storage, magnetic materials design and spectroscopic studies of biological objects. Compared to other N-oxyl radicals, oxime radicals (or iminoxyl radicals) have been underestimated for a long time as useful intermediates for organic synthesis, despite the fact that their precursors, oximes, are extremely widespread and easily available organic compounds. Furthermore, oxime radicals are structurally exceptional. In these radicals, the N–O• fragment is connected to an organic moiety by a double bond, whereas all other classes of N-oxyl radicals contain an R2N–O• fragment with two single C–N bonds. Although oxime radicals have been known since 1964, their broad synthetic potential was not recognized until the last decade, when numerous selective reactions of oxidative cyclization, functionalization, and coupling mediated by iminoxyl radicals were discovered. This review is focused on the synthetic methods based on iminoxyl radicals developed in the last ten years and also contains some selected data on previous works regarding generation, structure, stability, and spectral properties of these N-oxyl radicals. The reactions of oxime radicals are classified into intermolecular (oxidation by oxime radicals, oxidative C–O coupling) and intramolecular. The majority of works are devoted to intramolecular reactions of oxime radicals. These reactions are classified into cyclizations involving C–H bond cleavage and cyclizations involving a double C=C bond cleavage.

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α‐Oxo‐Iminoxyls of Isoxazolones, Pyrazolones and 1,2,3‐Triazolone

et al. 2015

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A series of α‐oxo‐iminoxyls was obtained by PbO2 oxidation of 4‐oximinoisoxazol‐5(4H)‐ones, 4‐oximinopyrazol‐5(4H)‐ones, and 1‐phenyl‐4‐oximino‐1,2,3‐triazol‐5(4H)‐one and characterized by electron spin resonance spectroscopy in conjunction with DFT calculations of structures, energies, and hyperfine coupling constants. The iminoxyls are σ‐radicals existing largely in the Z configuration with respect to the C=O group, but minor amounts of the E isomers were observable in several cases. Couplings of the free‐radical electron with N1, N2, N3, C4 and C5 ring nuclei as well as the imine nitrogen N6 were observed, and some isomers were also observed to couple with a CH3 group in position 3 and with the ortho‐H atoms of an aryl group in position 3. The lower energies of the Z isomers relative to the E isomers can be ascribed to a stabilizing interaction between a singly occupied orbital on the oxime oxygen and a lone pair orbital on the carbonyl oxygen.

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Spectral and kinetic measurements on a series of persistent iminoxyl radicals

Cited by 10 publications

References 27 publications

The Only Stable Organic Sigma Radicals: Di‐ tert ‐Alkyliminoxyls

The Only Stable Organic Sigma Radicals: Di‐ tert ‐Alkyliminoxyls

Oxime radicals: generation, properties and application in organic synthesis

α‐Oxo‐Iminoxyls of Isoxazolones, Pyrazolones and 1,2,3‐Triazolone

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Spectral and kinetic measurements on a series of persistent iminoxyl radicals

Cited by 10 publications

References 27 publications

The Only Stable Organic Sigma Radicals: Di‐ tert ‐Alkyliminoxyls

The Only Stable Organic Sigma Radicals: Di‐ tert ‐Alkyliminoxyls

Oxime radicals: generation, properties and application in organic synthesis

α‐Oxo‐Iminoxyls of Isoxazolones, Pyrazol­ones and 1,2,3‐Triazolone

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α‐Oxo‐Iminoxyls of Isoxazolones, Pyrazolones and 1,2,3‐Triazolone