Substitution reactions which proceed via radical anion intermediates. 20. Replacement of the nitro group by hydrogen

Kornblum, Nathan; Carlson, Stephen C.; Smith, Ronald G.

doi:10.1021/ja00497a028

Cited by 60 publications

(19 citation statements)

References 9 publications

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“…Hebting et al (2003) proposed an S RN 1 mechanism for the replacement of the sulfhydryl group with hydrogen (Scheme 1), analogous to the replacement of nitro and thioether groups with hydrogen following reaction with thiolate anions (Kornblum et al, 1978(Kornblum et al, , 1979. The first step is suggested to involve single electron transfer (SET) from a hydrogen sulfide anion to the sulfhydryl group of the thiol intermediate.…”

Section: Mechanismmentioning

confidence: 99%

“…Replacement of thioether groups with hydrogen was found to be slow (Kornblum et al, 1979), a fact that is probably reflected in the low yields obtained for the products of the reduction observed in this and previous studies (Hebting et al, 2003(Hebting et al, , 2006. Notably, the reduction of the C-3 vinyl substituent of pphorb a occurs at much lower temperatures (room temp and 4°C), over shorter timescales (4 d) and forms mpphorb a in apparently higher yields than the reduction of b-carotene and the reductive desulfurisation of phytenethiol (Hebting et al, 2003(Hebting et al, , 2006.…”

Section: Mechanismmentioning

confidence: 99%

“…Our findings clearly demonstrate that H 2 S can initiate the reduction of the C-3 vinyl substituent, providing firm evidence for an abiotic route to the formation of C-3 ethyl-containing chlorins and porphyrins in the natural environment. Given the evidence to support replacement of thioether groups with hydrogen in the presence of sulfide (Kornblum et al, 1979), C-3 1 thioether derivatives of chlorophyll a, identified in Recent Antarctic sediments (Squier et al, 2003(Squier et al, , 2004, may also be considered as potential intermediates in the reduction of the C-3 vinyl substituent. Furthermore, the involvement of H 2 S in the formation of mpphorb a raises questions as to whether the reduction observed by Spooner et al (1995) was the result of direct bacterial action.…”

Section: Significancementioning

confidence: 99%

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Low temperature abiotic formation of mesopyrophaeophorbide a from pyrophaeophorbide a under conditions simulating anoxic natural environments

Pickering

Keely

2011

Geochimica et Cosmochimica Acta

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Section: Mechanismmentioning

confidence: 99%

Section: Mechanismmentioning

confidence: 99%

Section: Significancementioning

confidence: 99%

See 1 more Smart Citation

Low temperature abiotic formation of mesopyrophaeophorbide a from pyrophaeophorbide a under conditions simulating anoxic natural environments

Pickering

Keely

2011

Geochimica et Cosmochimica Acta

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“…Other mechanisms including these radical-anion intermediates have also been reported e.g. SET^ (substitution, electron transfer, second order) [402], and reduction by dihydrobenzylnicotinamide [403], trialkyltin hydride [404], or methane thiolate [405]. All these mechanisms have an initial step of electron capture by the x-substituted nitro compounds to yield an intermediate radical- .…”

Section: Alkenesmentioning

confidence: 94%

Electron‐transfer Reactions of Aromatic Compounds

Gescheidt¹,

Khan²

2001

Electron Transfer in Chemistry

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Aromatic molecules are inclined to undergo electron-transfer reactions. The additional charges introduced by the electron-transfer process are efficiently stabilized by delocalization. Nevertheless rearrangements of the molecular skeleton or followup reactions can occur. The course of the electron-transfer reactions and the properties of the species thus formed are the subject of this section.In particular, we concentrate on the species formed after an one-electron transfer reaction. Starting from closed-shell diamagnetic precursors, paramagnetic stages, i.e. radical cations or radical anions are formed in this first step. To understand the properties and reactivity of these species, detailed knowledge in terms of charge and spin delocalization and electronic structure is an important prerequisite. This information is preferably derived from electronic and paramagnetic resonance (EPR and electron-nuclear multiple resonance-techniques such as ENDOR or Triple spectroscopy). It has recently been shown that the experimental results can be substantiated by the use of quantum-chemical calculations. In addition to Hartree-Fock-based ab initio procedures, calculations on the density-functional level of theory have been established as rather efficient tools. Therefore, before representing examples of electron-transfer-generated radicals a short survey of the computational methods is given.Another substantial factor directing the kinetic and thermodynamic stability of charged radicals is ion pairing. This phenomenon, although well established for many years, is often not directly distinct in experiments. To establish the importance of ion pairing, or, in other words, supramolecular interactions, a separate introductory chapter is dedicated to these aspects.The references are selected particularly from recent publications, without, however, ignoring some 'classical' contributions. In some sections topics are included which do not strictly represent aromatic molecules but involve interactions of ztype orbitals.

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“…Tanner, Blackburn, and Diaz [65] have reported the reduction {trialkyltin hydride) of tertiary nitro groups involves an electron transfer chain mechanism as shown below (Scheme 6). The reduc tion of a tertiary nitro group by the anion of methanethiol has been proposed to proceed via a similar mechanism as described above [66]. Table 7).…”

Section: Mechanistic Considerations For the Formation Of Dimers From mentioning

confidence: 85%

Free-radical clocks in the aliphatic S[subscript RN]1 process and reactions of nucleophiles with 1,1-dinitro-2,2-diphenylethylene

Dedolph

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Substitution reactions which proceed via radical anion intermediates. 20. Replacement of the nitro group by hydrogen

Cited by 60 publications

References 9 publications

Low temperature abiotic formation of mesopyrophaeophorbide a from pyrophaeophorbide a under conditions simulating anoxic natural environments

Low temperature abiotic formation of mesopyrophaeophorbide a from pyrophaeophorbide a under conditions simulating anoxic natural environments

Electron‐transfer Reactions of Aromatic Compounds

Free-radical clocks in the aliphatic S[subscript RN]1 process and reactions of nucleophiles with 1,1-dinitro-2,2-diphenylethylene

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