239449-35-5Relevant academic research and scientific papers
Absolute rate constants for SN1-like ionization reactions in zeolites: Determination of zeolite ionizing power
Ortiz, Wendy,Cozens, Frances L.,Schepp, Norman P.
, p. 531 - 534 (1999)
(Formula presented) A kinetic probe molecule has been developed to investigate the absolute ionizing power of cation-exchanged (LiY, NaY, KY, RbY, and CsY) Y-zeolites. The probe, the 2-chloro-1-(4-methoxyphenyl)ehtyl radical, was generated within the supe
Comparison of Activation Parameters for Ionization Reactions within Zeolites and in Aqueous Solution
Schepp, Norman P.,Monk, Wendy,Cozens, Frances L.
, p. 1012 - 1013 (2004)
Absolute rate constants for the ionization of chloride from the 2-chloro-1-(4-methoxyphenyl)ethyl radical are measured in aqueous methanol and in alkali-metal cation zeolites as a function of temperature. The absolute rate constants are very fast in the two distinct media. However, the activation parameters are considerably different. In solution, the reaction proceeds with low enthalpies of activation and large, negative entropies of activation, while in zeolites, the reaction is characterized by significantly higher activation enthalpies and large, positive entropies of activation. These differences reveal that the fundamental factors allowing for such rapid reactions are not the same in the two media. Copyright
Dynamics of ionization reactions of β-substituted radicals, substituent and solvent effects
Cozens, Frances L.,O'Neill, Melanie,Bogdanova, Roumiana,Schepp, Norman
, p. 10652 - 10659 (2007/10/03)
The dynamics of reactions of carbon-centered 1-arylalkyl radicals with bromine or chlorine attached to the carbon adjacent (β) to the radical center have been examined using nanosecond laser flash photolysis. The primary reaction of the radicals containing the electron-donating 4-methoxy group on the phenyl ring is highly dependent on the solvent composition. In weakly ionizing solvents such as acetonitrile, the radicals decay in a second-order manner indicating that coupling of two radical centers is the primary mode of radical decay. However, when the ionizing ability of the solvent is increased by addition of water, 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), or 2,2,2-trifluoroethanol (TFE), heterolysis of the β-substituent becomes the dominant mode of decay. The occurrence of the heterolysis reaction is demonstrated unambiguously by direct observation of the radical cation produced as the primary, heterolysis product. The rate constants for and yield of the heterolysis reaction are found to be dependent on both the solvent ionizing ability and radical structure. In neat water or neat HFIP the reactions become extremely fast and occur with rate constants in the 107 s-1 to ≤ 108 s-1 range. For the β-bromophenethyl and β-bromo-4-methyphenethyl radicals, no heterolysis is observed even under strongly ionizing conditions, indicating that the rate constant for ionization is strongly influenced by the substituent on the phenyl ring. For radicals with an additional β-phenyl substituent, rapid heterolysis takes place leading to the formation of the stilbene radical cation. The formation of a radical/radical cation equilibrium was observed under the appropriate conditions only for the 4-methoxyphenethyl radical derivatives.
Reactivities of radical cations: Characterization of styrene radical cations and measurements of their reactivity toward nucleophiles
Johnston,Schepp
, p. 6564 - 6571 (2007/10/02)
A variety of substituted styrene radical cations (2) have been generated by 266-or 308-nm photoionization of the parent olefin in polar solvents or by electron-transfer quenching of triplet chloranil. The rate constant for decay of most of the radical cat
