A theoretical approach to the Birch reduction. Structures and stabilities of the radical anions of substituted benzenes

The electron affinities of 14 substituted nitrobenzenes including nitrobiphenyls were determined by measurement of electron transfer equilibria [1] in the gas phase with a pulsed high pressure mass spectrometer: A− + B = A + B− [1]. These data, when combined with previous determinations from this laboratory, lead to electron affinities for 35 substituted nitrobenzenes and provide a comprehensive data set for the examination of substituent effects. The data are used to derive Taft gas-phase substituent parameters. A qualitative discussion based on frontier orbital molecular theory examines the substituent effect on the benzene and nitrobenzene LUMOs. The lifetimes for electron autodetachment from excited nitrobenzene negative ions, (A−)*, studied earlier by Christophorou, are examined in light of the present electron affinity data. Keywords: electron affinities, substituent effects, frontier orbital treatment, electron autodetachment from nitrobenzene radical anions.

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“…[5], was close to identical to the substituent effect on the gas-phase acidities of phenols, 6A0phoH, see eq. [61.…”

Section: Discussionsupporting

confidence: 54%

Electron affinities of substituted nitrobenzenes

Chowdhury¹,

Kishi²,

Dillow³

et al. 1989

Can. J. Chem.

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“…The reduction of benzoyl-CoA to a nonaromatic cyclic compound via an Azoarcus-like benzoylCoA reductase is catalyzed by an ATP-dependent two-electron transfer to the aromatic ring via ferredoxin (43). The transfer of electrons to the benzene ring requires electrons at a very low redox potential (6). In Azoarcus evansii, ferredoxin serves as the electron donor for the benzoyl-CoA reductase (21) and the oxidized ferredoxin is reduced by a 2-oxoglutarate:acceptor oxidoreductase in combination with a NADPH:acceptor oxidoreductase.…”

Section: Discussionmentioning

confidence: 99%

Combined Genomic and Proteomic Approaches Identify Gene Clusters Involved in Anaerobic 2-Methylnaphthalene Degradation in the Sulfate-Reducing Enrichment Culture N47

et al. 2010

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The highly enriched deltaproteobacterial culture N47 anaerobically oxidizes the polycyclic aromatic hydrocarbons naphthalene and 2-methylnaphthalene, with sulfate as the electron acceptor. Combined genome sequencing and liquid chromatography-tandem mass spectrometry-based shotgun proteome analyses were performed to identify genes and proteins involved in anaerobic aromatic catabolism. Proteome analysis of 2-methylnaphthalene-grown N47 cells resulted in the identification of putative enzymes catalyzing the anaerobic conversion of 2-methylnaphthalene to 2-naphthoyl coenzyme A (2-naphthoyl-CoA), as well as the reductive ring cleavage of 2-naphthoyl-CoA, leading to the formation of acetyl-CoA and CO 2 . The glycyl radical-catalyzed fumarate addition to the methyl group of 2-methylnaphthalene is catalyzed by naphthyl-2-methyl-succinate synthase (Nms), composed of ␣-, ␤-, and ␥-subunits that are encoded by the genes nmsABC. Located upstream of nmsABC is nmsD, encoding the Nms-activating enzyme, which harbors the characteristic [Fe 4 S 4 ] cluster sequence motifs of S-adenosylmethionine radical enzymes. The bns gene cluster, coding for enzymes involved in beta-oxidation reactions converting naphthyl-2-methyl-succinate to 2-naphthoyl-CoA, was found four intervening open reading frames further downstream. This cluster consists of eight genes (bnsABCDEFGH) corresponding to 8.1 kb, which are closely related to genes for enzymes involved in anaerobic toluene degradation within the denitrifiers "Aromatoleum aromaticum" EbN1, Azoarcus sp. strain T, and Thauera aromatica. Another contiguous DNA sequence harbors the gene for 2-naphthoyl-CoA reductase (ncr) and 16 additional genes that were found to be expressed in 2-methylnaphthalene-grown cells. These genes code for enzymes that were supposed to catalyze the dearomatization and ring cleavage reactions converting 2-naphthoyl-CoA to acetylCoA and CO 2 . Comparative sequence analysis of the four encoding subunits (ncrABCD) showed the gene product to have the closest similarity to the Azoarcus type of benzoyl-CoA reductase. The present work provides the first insight into the genetic basis of anaerobic 2-methylnaphthalene metabolism and delivers implications for understanding contaminant degradation.Polycyclic aromatic hydrocarbons (PAHs) are constantly released into the environment by anthropogenic activities such as industrial use or by accidental contamination. Due to the low chemical reactivity caused by the resonance energy of the aromatic ring structure and the low bioavailability of PAHs, they are persistent in the environment (15). The understanding of microbial metabolic capabilities in terms of anaerobic PAH degradation is in its infancy. However, natural amelioration of contaminated sites relies on the degradation capacities of microorganisms, and therefore, it is an essential prerequisite to broaden knowledge about the microorganisms involved and their potentials concerning PAH breakdown.Numerous microorganisms that can degrade PAHs under aerobic conditions have alread...

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“…The electron withdrawing character of the acid group of benzoate stabilizes the anion radical at carbon 1 of the ring; the second electron adds in para position because of electrostatic repulsion. However, in the presence of a strong base, the thermodynamically more stable conjugated 1,5-diene can be obtained (25,26). This base-catalyzed rearrangement seems to occur in the catalytic cycle of T. aromatica.…”

Section: Discussionmentioning

confidence: 99%