54668-31-4Relevant articles and documents
Entropy control of the cross-reaction between carbon-centered and nitroxide radicals
Sobek,Martschke,Fischer
, p. 2849 - 2857 (2007/10/03)
Absolute rate constants for the cross-coupling reaction of several carbon-centered radicals with various nitroxides and their temperature dependence have been determined in liquids by kinetic absorption spectroscopy. The rate constants range from 5 M-1 s-1 to 2.3 × 109 M-1 s-1 and depend strongly on the structure of the nitroxide and the carbon-centered radical. Grossly, they decrease with increasing rate constant of the cleavage of the corresponding alkoxyamine. In many cases, the temperature dependence shows a non-Arrhenius behavior. A model assuming a short-lived intermediate that is hindered to form the coupling product by an unfavorable activation entropy leads to a satisfactory analytic description. However, the behavior is more likely due to a barrierless single-step reaction with a low exothermicity where the free energy of activation is dominated by a large negative entropy term.
An Electron Spin Resonance Investigation of Free Radicals with Oxigen- and Sulphur-containing Substituents
Beckwith, Athelstan L. J.,Brumby, Steven
, p. 1801 - 1808 (2007/10/02)
Electron spin resonance (e.s.r.) spectra have been recorded during the photolysis of di-t-butyl peroxide in the presence of a number of organic substrates with oxigen- 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 radical generated.Bis(methylthio)methane (2) gives rise to tris(methylthio)methyl radicals (5a), in addition to the two species expected by direct abstraction.Tris(methylthio)methane (5) gives rise to tris(methylthio)methyl radicals (5a) only, which from the measured α(13)C 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 two cyclic radicals suggest that relatively small deviations from a suitable planar conformation can significantly diminish the importance of the captodative effect.
Gas-Phase Nucleophilic Reactivities of Phenylnitrene (PhN-*) and Sulfur Anion Radicals (S-/.) at sp3 and Carbonyl Carbon
McDonald, Richard N.,Chowdhury, A. Kesem
, p. 198 - 207 (2007/10/02)
The reactions of PhN-/. with a series of carbonyl-containing molecules (aldehydes, ketones, and esters) were shown to proceed via an addition/fragmentation mechanism, PhN-* + R2C=O -> -)R2> -> PhN=C(O-)R + *R, producing various acyl anilide anion products.In several cases, the tetrahedral intermediate anion radicals were observed as minor ions.The intrinsic reactivity of the carbonyl-containing molecules was aldehydes > ketones > esters, where similar R groups were involved.The overall exothermicities of these reactions did not appear to play the major role in determining the relative rates (krelC=O) for these reactions.From the reaction of PhN-* with cyclobutanone, a new type of anion radical, PhN=C(O-)CH2* (m/z 133) (+ C2H4) was produced; the loss of C2H4 was considered due to the ring strain in the ketone.With cyclopentanone, cyclohexanone, and cycloheptanone, the anion radicals PhN=C(O-)(CH2)n* (n = 4-6) were the exclusive product ions.PhN-* was shown to be a poor nucleophile in SN2 displacement reactions with CH3X molecules (X = Cl, Br, O2CCF3).S-* was shown to exhibit modest SN2 nucleophilicity with CH3Cl and CH3Br.The reactions of S-* with CF3CO2R proceed via both SN2 displacement and carbonyl addition/fragmentation mechanisms: with R = CH3, the anion products were 65percent CF3CO2- and 35percent CF3COS-; from R = C2H5, the product ions were 4percent CF3CO2- and 96percent CF3COS-.These data yield the ratio kCH3/kC2H5 = 16 for SN2 displacement by S-* at these alkyl groups.The reactions of PhN-* with CO2, COS, CS2, and O2 are also reported.The reaction of PhN-* with CS2 to produce S-* as a major channel was used as the source of this atomic anion radical.In several reactions occuring at nearly the collison limit, selectivity was observed for (a) which of two reaction centers were attacked to give products and (b) which of two mechanisms would be dominant in the overall reaction.
Hydrogen Abstraction from (2H3)methyl Acetate by Methyl and Trifluoromethyl Radicals
Arthur, Neville L.,Newitt, Paula J.
, p. 727 - 735 (2007/10/02)
A study of hydrogen abstraction from CH3COOCD3 by CH3 radicals in the temperature range 113-232 deg C, and by CF3 radicals in the range 83-212 deg C, has yielded data on the reactions: CH3 + CH3COOCD3 CH4 + CH2COOCD3 (1), CH3 + CH3COOCD3 CH3D + CH3COOCD2 (2), CF3 + CH3COOCD3 CF3H + CH2COOCD3 (3), CF3 + CH3COOCD3 CF3D + CH3COOCD2 (4). The corresponding rate constants, based on the values 1013.34and 1013.36 cm3 mol-1 s-1 for the recombination of CH3 and CF3 radicals, respectively, are given by (k in cm3 mol-1 s-1 and E in J mol-1): log k1 = (11.31 +/- 0.12) - (43500 +/- 1030)/19.145 T (1), log k2 = (11.33 +/- 0.08) - (53460 +/- 640)/19.145 T (2), log k3 = (11.12 +/- 0.06) - (34260 +/- 450)/19.145 T (3), log k4 = (10.93 +/- 0.12) - (38650 +/- 900)/19.145 T (4).These results lead to kinetic isotope effects at 400 K for attack on the acetyl group of 11, for the CH3 reaction, and 24, for the CF3 reaction, thus confirming the values we obtained previously.For attack on the methoxy group, the kinetic isotope effects are 8 and 4, for the CH3 and CF3 reactions, respectively.
Reactions of Trifluoromethyl Radicals. V. Hydrogen Abstraction from Methyl Acetate and Methyl (2H3)Acetate
Arthur, Neville L.,Newitt, Paula J.
, p. 1437 - 1446 (2007/10/02)
Hydrogen abstraction by CF3 radicals from CH3COOCH3 and CD3COOCH3 has been studied in the temperature range 78-242 deg C, and data have been obtained for reactions: CF3 + CH3COOCH3 -> CF3H + (3), CF3 + CH3COOCH3 -> CF3H + CH2COOCH3 (4), CF3 + CD3COOCH3 -> CF3D + CD2COOCH3 (6), CF3 + CD3COOCH3 -> CF3H + CD3COOCH2 (7).The corresponding rate constants, based on the value of 1013.36 cm3mol-1s-1 for the recombination of CF3 radicals, are given by ( k in cm3mol-1s-1 and E in J mol -1): logk3 = (11.52+/-0.05) - (35430+/-380)/19.145T (3), logk4 = (11.19+/-0.07) - (34680+/-550)/19.145T (4), logk6 = (11.34+/-0.06) - (46490+/-490)/19.145T (6), logk7 = (11.26+/-0.05) - (36440+/-400)/19.145T (7).At 400 K, 59percent of abstraction occurs from the acetyl group, and 41percent from the methoxy group.The kinetic isotope effect at 400 K for attack on the acetyl group is 25, due mainly to a difference in activation energies.
