- Establishment of heterolytic and homolytic Y-NO2 bond dissociation energy scales of nitro-containing compounds in acetonitrile: Chemical origin of NO2 release and capture
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(Chemical Equation Presented) The first heterolytic and homolytic N(O)-NO2 bond dissociation energy scales of three types Y-nitro (Y = N, O) compounds and corresponding radical anions in acetonitrile were established by using titration calorimetry combined with relevant electrochemical data through proper thermodynamic cycles.
- Li, Xin,Zhu, Xiao-Qing,Zhang, Fan,Wang, Xiao-Xiao,Cheng, Jin-Pei
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p. 2428 - 2431
(2008/09/20)
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- Lewis acid assisted permanganate oxidations
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Lewis acids combine with permanganate in acetone solutions to form a complex that has enhanced oxidizing capabilities. The use of Lewis acids under these conditions to promote permanganate oxidations is superior to the use of Bronsted acids because the latter promote enolization of the solvent and subsequent unproductive reduction of the oxidant. The products obtained from a variety of alkenes, alkynes, arenes, sulfides, alcohols and ethers have been identified and probable reaction mechanisms proposed.
- Lai, Sheng,Lee, Donald G.
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p. 9879 - 9887
(2007/10/03)
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- A kinetic evaluation of carbon-hydrogen, carbon-carbon, and carbon-silicon bond activation in benzylic radical cations
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A detailed study of the competition between C-C, C-H, and C-Si bond fragmentation in a series of 4-methoxy-α-substituted toluene radical cations (1.+), involving both product studies and kinetic analysis, is presented. C-C bond fragmentation occurs with several radical cations in acetonitrile. The rate constants for such processes, determined by laser flash photolysis, varied from 2.8 x 104 (1c.+) to 1.53 x 106 (1f.+) s-1. The activation parameters for C-C bond fragmentation are characterized by low activation enthalpies on the order of 30 kJ mol-1 and negative activation entropies in the range -34 to -55 J mol-1 K-1. Deprotonation of the radical cations is always a second-order process induced by nucleophiles [cerium(IV) ammonium nitrate (CAN) or nitrate anion], with second-order rate constants from 7.7 x 107 (1h.+) to 8.8 x 108 (1i.+) M-1 s-1 in neat acetonitrile (CAN assisted) and from 0.4 x 108 (1j.+) to 7.1 x 108 (1i.+) M-1 s-1 in the presence of nitrate anion. The rate constant for nitrate-induced decarboxylation was higher, 13.6 x 108 M-1 s-1 (1d.+). In a few cases C-C (1e.+, 1f.+) and C-Si (1g.+) fragmentations occurred, also as second-order processes induced by nitrate, with rate constants from 4.4 x 108 (1f.+) to 8.2 x 108 (1g.+) M-1 s-1. ΔH and ΔS had opposing influences on C-H and C-C fragmentation, and in the case of 1e.+ a temperature-dependent product distribution was obtained. The activation parameters for the observed C-H, C-C, and C-Si fragmentations have been compared, and suggest a rationale for the mechanisms and selectively of such processes in radical cations.
- Freccero, Mauro,Pratt, Albert,Albini, Angelo,Long, Conor
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p. 284 - 297
(2007/10/03)
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- Photoinduced electron transfer reactions of benzyl phenyl sulfides promoted by 9,10-dicyanoanthracene
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The photoinduced oxidation of benzyl phenyl sulfides 1-3 has been investigated in MeCN using 9,10-dicyanoanthracene as sensitizer in the presence of O2. In this reaction a sulfide radical cation is formed, which undergoes one or more of the three main reaction pathways opened to these species: C-S bond cleavage, C-H bond cleavage and S-oxidation. The former route (leading to benzylic products) was observed with all the substrates investigated, whereas the second (leading to benzaldehydes) operates only with 1 and 2. Formation of sulfoxides was found solely in the photooxidation of 1. The influence of substrate structures on the relative contribution of the three pathways as well as the role of O2- in this respect are discussed.
- Baciocchi, Enrico,Crescenzi, Cristina,Lanzalunga, Osvaldo
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p. 4469 - 4478
(2007/10/03)
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