Restricted Rotation in α-Carbonyl Radicals

Foster, Terry; Klapstein, Dieter; West, Paul R.

doi:10.1139/v74-082

Cited by 16 publications

(10 citation statements)

References 6 publications

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“…spectra did not show evidence for interconversion between (lla) and (llb), even at +34"C. In contrast, the spectra of (17), and other alkanoyl methyl radicals which do not have dative s u b ~t i t u e n t s , ~~ conform to the fast exchange limit at this temperature, although there is evidence that rotation may be more strongly hindered in aqueous media. 43 The observations seem to be consistent with the view that the captodative effect increases the barriers to internal rotation.…”

Section: Mef Osupporting

confidence: 80%

An electron spin resonance investigation of free radicals with oxygen- and sulphur-containing substituents

Beckwith¹,

Brumby²

1987

J. Chem. Soc., Perkin Trans. 2

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Electron spin resonance (e.s.r.) spectra have been recorded during the photolysis of di-tbutyl peroxide in the presence of a number of organic substrates with oxygen-and sulphur-containing functional groups. By hydrogen-atom abstraction, many of the substrates yield more than one species of free radical, the relative concentrations of which have been estimated. These relative concentrations are influenced by the electrophilic character of the t-butoxyl radical, and by the stabilities of the radicals generated.Bis(methy1thio)methane (2) gives rise to tris(methy1thio)methyl radicals (5a), in addition to the two species expected by direct abstraction. Tris( methy1thio)methane (5) gives rise to tris(methy1thio)methyl radicals (5a) only, which, from the measured a13C hyperfine splitting constant, appear to be approximately planar. Several of the substrates used give rise to captodative free radicals. The data indicate that alkylcarbonyl groups are more effective than the methoxycarbonyl group in the capto role. The acyclic captodative radicals all exist in two distinct conformations, the likely geometries of which are discussed. Observations on t w o cyclic radicals suggest that relatively small deviations from a suitable planar conformation can significantly diminish the importance of the captodative effect.We are interested in the factors which influence the rates of abstraction of hydrogen atoms from molecules by free radicals such as t-butoxyl. In this connection, we have recorded e.s.r. spectra during the photolysis of solutions of substrates (1)-( 14) CH,(OMe), (1) MeSCH,OMe (3) CH(SMe), Radical 'CH(OMe), (la) 'CH,OCH,OMe (lb) 'CH(SMe), (2a) 'CH,SCH,SMe (2b) 'C(SMe), (5a) 'CH(0Me)SMe (321) 'CH,SCH,OMe (3b) 'CH,OCH,SMe (3c) 'C(OMe), (4a) 'CH,OCH(OMe), (4b) 'C(SMe), (5a) 'CH(OMe)CH,OMe (6a) 'CH,O(CH,),OMe (6b) ( 6 4 (6b) 'CH(0Me)OCOMe (7a) 'CH,OCH,OCOMe (7b) Rel. conc.8.0

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Section: Mef Osupporting

confidence: 80%

An electron spin resonance investigation of free radicals with oxygen- and sulphur-containing substituents

Beckwith¹,

Brumby²

1987

J. Chem. Soc., Perkin Trans. 2

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“…Most likely they are due to the 1-formylcyclohexyl radicals generated by abstraction of the tertiary H-atoms adjacent to the formyl groups. The g- factor of the analogous Me 2 C( • )CHO radical is 2.0045, in close agreement …”

Section: Referencessupporting

confidence: 63%

“…The triplet multiplicity was unexpected for a cyclohexylacyl radical containing a single β-hydrogen . The spectrum showed small additional features, marked A in Figure a,b, on either side of the triplet, which have a separation ( w ) of 8.9 G. A broad line at lower field ( g = 2.0046) was also observed. , …”

mentioning

confidence: 90%

Axial and Equatorial Cyclohexylacyl and Tetrahydropyranyl-2-acyl Radicals. An Experimental and Theoretical Study

DiLabio

Roydhouse

et al. 2004

Org. Lett.

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Axial and equatorial cyclohexylacyl and tetrahydropyranyl-2-acyl radicals gave distinct EPR spectra thanks to surprisingly large beta-hydrogen atom hyperfine splittings that enabled them to be characterized and monitored. DFT computations indicated that the axial species (X = CH(2)) had a higher barrier to rotation about the (O)C(alpha)-C(beta) bond. The computed difference Delta H degrees for the axial and equatorial radicals (R = H, X = CH(2)) was 0.8 kcal mol(-)(1).

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“…Kinetics of Radical Decay. At temperatures of -50 °C and lower, radical la decays with second-order kinetics at a rate Journal of the American Chemical Society / 99:13 / June 22,1977 that is close to the diffusion-controlled limit (see Table II). The decay process must be a dimerization since 1,2-dibenzoylethane was isolated (see Experimental Section).…”

Section: Results and Interpretationmentioning

confidence: 91%

Kinetic applications of electron paramagnetic resonance spectroscopy. 30. Rearrangement of the benzoylmethyl radical

Brunton¹,

McBay²,

Ingold³

1977

J. Am. Chem. Soc.

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Restricted Rotation in α-Carbonyl Radicals

Cited by 16 publications

References 6 publications

An electron spin resonance investigation of free radicals with oxygen- and sulphur-containing substituents

An electron spin resonance investigation of free radicals with oxygen- and sulphur-containing substituents

Axial and Equatorial Cyclohexylacyl and Tetrahydropyranyl-2-acyl Radicals. An Experimental and Theoretical Study

Kinetic applications of electron paramagnetic resonance spectroscopy. 30. Rearrangement of the benzoylmethyl radical

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