Mechanistic Studies of Ce(IV)-Mediated Oxidation of β-Dicarbonyls: Solvent-Dependent Behavior of Radical Cation Intermediates
作者:Jingliang Jiao、Yang Zhang、James J. Devery、Luna Xu、Jennifer Deng、Robert A. Flowers
DOI:10.1021/jo0625406
日期:2007.7.1
The Ce(IV)-initiated oxidation of synthetically relevant β-diketones and β-keto silyl enol ethers was explored in three solvents: acetonitrile, methylene chloride, and methanol. The studies presented herein show that the rate of reaction between Ce(IV) and the substrates is dependent upon the polarity of the solvent. Thermochemical studies and analysis are interpreted to be consistent with transition
Two-color multiphoton dissociation/ionization of jet-cooled CrIII(acac)3 and Cr0(CO)6. Appearance energies of Cr atom
作者:Naohiko Mikami、Rie Ohki、Hiroaki Kido
DOI:10.1016/0301-0104(88)87115-5
日期:1988.11
fragment other than the Cr atom is produced by the two-photon dissociation and that the threshold energy for Cr atom generation is about 78500 cm−1 (9.73 eV). The result suggests that the neutral Cr atom originates directly from the super-excited state which is the neutral excited state lying at about 2.27 eV higher than the ionization potential of CrIII(acac)3. For Cr0(CO)6, the production of the coordinatively
Estimation of Bond Dissociation Energies and Radical Stabilization Energies by ESR Spectroscopy
作者:Jochen J. Brocks、Hans-Dieter Beckhaus、Athelstan L. J. Beckwith、Christoph Rüchardt
DOI:10.1021/jo971940d
日期:1998.3.1
Correlations of various indices of the stability and reactivity of carbon-centered radicals with ESR hyperfine splitting constants have been examined. For a large number of mono-and disubstituted radicals there is a moderately good linear correlation of alpha-proton hyperfine splitting constants (a(H-alpha) with radical stabilization enthalpies (RSE) and with BDE(C-H), the C-H bond-dissociation energies for the corresponding parent compounds determined from thermodynamic and kinetic studies of C-C homolysis reactions. There is a similarly satisfactory linear correlation of a(H-alpha) with BDE(C-H) determined by Bordwell's electrochemical and acidity function method. In all cases the correlations fail for nonplanar radicals. As expected, beta-proton hyperfine splitting constants (a(HbetaMe)) for radicals with a freely rotating methyl substituent are less sensitive to deviations from planarity and give better linear correlations with RSE and BDE(C-H). The correlations cover a range of more than 20 kcal/mol and are reliable predictors of RSE and BDE(C-H) for a variety of radicals including captodative species. However, the correlations fail for significantly nonplanar radicals and for radicals with cyclic delocalized systems, e.g., cyclopentadienyl. The ratio a(HbetaMe)/a(H-alpha for suitably substituted radicals provides an index of pyramidalization and allows one to decide for which compounds values of RSE and BDE(C-H) can be confidently estimated.
Broszkiewicz, R. K.; Soeylemez, T.; Schulte-Frohlinde, D., Zeitschrift fur Naturforschung, Teil B: Anorganische Chemie, Organische Chemie, 1982, vol. 37, # 3, p. 368 - 375
作者:Broszkiewicz, R. K.、Soeylemez, T.、Schulte-Frohlinde, D.
DOI:——
日期:——
Nedelec, Jean-Yves; Lachaise, Isabelle; Nohair, Khaddouj, Bulletin de la Societe Chimique de France, 1995, vol. 132, # 8, p. 843 - 849
作者:Nedelec, Jean-Yves、Lachaise, Isabelle、Nohair, Khaddouj、Paugam, Jean Paul、Hakiki, Marjouba