103466-88-2Relevant academic research and scientific papers
Temperature Effects on Rates of Dehalogenation of Aromatic Anion Radicals
Meot-Ner (Mautner), M.,Neta, P.,Norris, Robert K.,Wilson, Karen
, p. 168 - 173 (2007/10/02)
The temperature dependence of the unimolecular dehalogenation of radical anions of nitrobenzyl halides and haloacetophenones was measured between -7 and 70 deg C.Activation parameters range from Ea=11.2-16.9 kcal/mol and log A=12.7-17.1.Both Ea and log A increase from p- to o-nitro radicals and from chloro to bromo radicals.Unfavorable steric effects that move the halogen atom out of the aromatic plane result in lowered A factors.In general, the variation of k294 with structure depends in a complex way on the combination of Ea and log A factors, which suggests caution in the evaluation of rate constants at one temperature.The fast unimolecular dissociation of (p-NO2C6H4CH2Br)(1-). (k294=4.6*105 s-1) allows measurement of the slower bimolecular electron transfer (C6H5NO2)(1-).+p-NO2C6H4CH2Br->(p-NO2C6H4CH2Br)(1-).+C6H5NO2 (k294=1.9*106 M-1 s-1).Both the activation energy and probability factor contribute to the slow rate, possibly due to a geometry change upon the reduction of ArNO2.Extending the temperature studies to supercooled solutions shows no discontinuity of the unimolecular rate constants near the phase transition temperatures.
Theory of Intramolecular Electron Transfer Reactions in Anion Radicals of Nitrobenzyl Halides
Miller, Kristine E.,Kozak, John J.
, p. 401 - 403 (2007/10/02)
Recently, we have suggested a lattice-based theory of chemical reactivity in which quantum and statistical mechanical arguments are combined to yield a method for calculating rate constants for certain classes of reactions.We present here the first concrete application of this theory and calculate the first-order rate constants for dehalogenation of the ortho-, meta-, and para-substituted nitrobenzyl chloride anion radicals.Our theoretical results are obtained by calculating the ? orbital spin populations of the anion radicals (MO calculations using the GAUSSIAN 82 series of programs), using the consequent values to distinguish the ortho, meta, and para sites, and then calculating the rate constants using a lattice statistical approach, the latter based on a theory presented recently.Apart from the limitations of the MO calculations and the neglect of solvent effects, the method involves no further assumptions or parameters.The theoretical estimates are in good agreement with the experimental rate constants.
Intramolecular Electron Transfer in the Anion Radicals of Nitrobenzyl Halides
Neta, P.,Behar, D.
, p. 4798 - 4802 (2007/10/02)
One-electron reduction of nitrobenzyl halides produces the anion radicals which subsequently undergo intramolecular electron transfer and decompose into nitrobenzyl radicals and halide ions.The optical absorption spectra of the initial anion radicals (λmax ca. 300-310 nm) and the subsequently formed nitrobenzyl radicals (λmax = 359 and 400 for the para and ortho, respectively) are quite intense (ε ca. 104 M-1 cm-1 in most cases) and significantly different.This enables identification of the various species and measurement of the rates of intramolecular electron transfer or C-X bond scission.The rates are 4*103, 1.7*105, and 5.7*105 s-1 for p-nitrobenzyl chloride, bromide, and iodide, respectively.The ortho derivatives decomposed nearly twice as rapidly while the meta decomposed much more slowly.The anion radical of p-nitrobenzyl bromide has pKa = 2.8, and the protonated form is found to undergo the intramolecular transfer ca. 60 times more slowly than the anion radical.The pattern of reactivity of the various anion radicals is rationalized in terms of spin density and charge distribution at the various positions on the ring and in terms of the electrophilicities of the halogens.
