2143-53-5Relevant articles and documents
Substituent Effects by Deuterium and Alkyl Groups and 13C Hyperfine Coupling Constants of Cyclopentadienyl Radicals as Studied by Electron Spin Resonance
Kira, Mitsuo,Watanabe, Mieko,Sakurai, Hideki
, p. 5202 - 5207 (1980)
ESR spectra of the parent and six substituted cyclopentadienyl radicals (RC5H4; R = H, D, Me, Et, i-Pr, t-Bu, Me3SiCH2), generated from the corresponding RC5H4SnMe3 by an SH2 attack on Sn with the photochemically generated tert-butoxy radical, have been recorded over the temperature range -95 to +24 deg C.Judging from the proton coupling constants, the electron-releasing perturbation of alkyl groups is in the order (CH3)3SiCH2 > CH3 > C2H5 > (CH3)2CH > (CH3)3C.Preferred conformations of these alkyl groups are discussed from the temperature effects on the spectra.Notably, the methyl group rotates freely, while the (CH3)3SiCH2 group has a fixed conformation in which the (CH3)3Si group eclipses the p orbital on the C1 atom of the cyclopentadienyl.The resonance-integral perturbation effect is more important than the Coulomb-integral perturbation in the deuterium substitution.Finally the coupling constants of 13C for CnHn (n = 5-8) radical species are discussed.
Davies,Tse
, p. 353 (1978)
Zandstra
, p. 612 (1964)
Furuyama et al.
, p. 237,239,243,244 (1971)
Ultrafast electron diffraction of transient cyclopentadienyl radical: A dynamic pseudorotary structure
Ihee, Hyotcherl,Feenstra, Jonathan S.,Cao, Jianming,Zewail, Ahmed H.
, p. 325 - 334 (2008/10/08)
Ultrafast electron diffraction (UED) is applied here in the study of the reaction of cylcopentadienyl cobalt dicarbonyl (CpCo(CO)2) which proceeds to give product structures. These structures were probed by picosecond electron pulses. The major product of the fragmentation was found to be the cyclopentadienyl radical. The dynamic nature of the radical was best represented by a pentagonal molecular structure having D5h symmetry with elevated mean amplitudes of vibration. Comparisons between theory and experiment are presented. The structure is that of the transition state between the compressed (dienylic) and the elongated (allylic) conformations but with longer bond distances, reflecting the dynamics of the pseudorotary surface.
Rate Constants for Termination and TEMPO Trapping of Some Resonance Stabilized Hydroaromatic Radicals in the Liquid Phase
Arends, I.W.C.E.,Mulder, P.,Clark, K.B.,Wayner, D.D.M.
, p. 8182 - 8189 (2007/10/02)
The rate constants for the termination reaction (2k1) of some resonance stabilized carbon centered radicals (SR.) derived from hydroaromatics (Sr. + SR. -> P) have been determined at 294 +/- 2 K by laser flash photolysis with UV-vis detection.The radicals were generated by hydrogen atom abstraction by t-BuO-radicals from the corresponding hydrocarbon (SRH + t-BuO. -> SR. + t-BuOH. k4).The extinction coefficients (e) of the SR., essential to calculate 2k1, were obtained using a relative kinetic technique.The change in 2k1 for the radicals derived from 1,4-cyclohexadiene, fluorine, 9,10-dihydroanthracene, diphenylmethane, tetralin, indan, indene, and phenol appeared to be modest; a range of 2k1 = 2-10 x 1E9 M-1 s-1 in mixtures of benzene and di-tert-butyl peroxide was observed.Most of the rate constants are near the diffusion controlled limit.In contrast, quenching the radicals with a persistent radical, 2,2,5,5-tetramethylpiperidin-1-oxyl (TEMPO), resulted in a larger variation of -1 s-1.The strength of the N-O bond formed in the latter process may have an important contribution to the observed rate constant.
