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The aim of this paper is to present a correct and complete mechanistic picture of nucleophilic substitution in nitroarenes based on the results obtained by theoretical calculations and experimental observations coming from numerous publications, reviews, and monographs. This work gives the theoretical background to the very well documented experimentally yet still ignored observations that the addition of nucleophiles to halo nitroarenes resulting in the formation of sH adducts, which under proper reaction conditions can be transformed into the product of the SNArH reaction, is faster than the competing process of addition to the carbon atom bearing a nucleofugal group (usually a halogen atom) resulting in the "classic" SNAr reaction. Only when the sH adduct cannot be transformed into the SNArH reaction product, SNAr reaction is observed. [ABSTRACT FROM AUTHOR]

Anions of nitroderivatives of thiophene and furan were subjected to the reactions with selected C-H acids in the gas phase. Various structures and reaction pathways were proposed for the observed ionic products. In general, the reactions of heteroaromatic anions with C-H acids may be divided into three groups, depending on the proton affinity difference between C-H acid's conjugate base and heteroaromatic anion (ΔPA). The proton transfer from C-H acid to heteroaromatic anion is a dominant process in the reactions for which ΔPA < 0 kcal mol, whereas the reactions with high ΔPA (ΔPA > 16 kcal mol) do not lead to any ionic products. The formation of σ-adducts and products of their further transformations according to the VNS, SAr, cine, and tele substitution mechanisms have been proposed for reactions with moderate ΔPA. The other possible mechanisms as S2 reaction, nucleophilic addition to the cyano group, ring-opening pathway, and halogenophilic reaction have also been discussed to contribute in the reactions between heteroaromatic anions and C-H acids. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

In the gas-phase reactions of halonitro- and dinitrophenide anions with X (X = F, Cl, Br, NO2) and NO2 groups in ortho or para position to each other with selected C-H acids: CH3CN, CH3COCH3, and CH3NO2, products of the SNAr-type reaction are formed. Nitrophenide anions are generated by decarboxylation of the respective nitrobenzenecarboxylate anions in ESI ion source and the SNAr reaction takes place either in the medium-pressure zone of the ion source or in the collision chamber of the triple quadrupole mass spectrometer. In the case of F, Cl, and NO2 derivatives, the main ionic product is the respective [NO2-Ph-CHR]− anion (R = CN, COCH3, NO2). In the case of Br derivatives, the main ionic product is Br− ion because it has lower proton affinity than the [NO2-Ph-CHR]− anion (for R = CN, COCH3). For some halonitrophenide anion C–H acid pairs of reactants, the SNAr reaction is competed by the formation of halophenolate anions. This reaction can be rationalized by the single electron-transfer mechanism or by homolytic C–H bond cleavage in the proton-bound complex, both resulting in the formation of the halonitrobenzene radical anion, which in turn undergoes –NO2 to –ONO rearrangement followed by the NO· elimination. [Copyright &y& Elsevier]

Di- and trinitrophenide anions generated by decarboxylation of the anions of 2,4-, 3,5-, and 2,6-dinitrobenzoic acids and 1,3,5-trinitrobenzoic acid in the medium-pressure region of an electrospray ion source react locally with various C-H acids delivered in the form of vapors mixed with the curtain gas, yielding anionic σ-adducts. Positive results were obtained for aliphatic aldehydes, ketones, esters and nitriles. All three dinitrobenzoic acids bearing NO2 groups in the meta position to each other gave the same σ-adducts which can be rationalized by a reaction sequence including proton transfer from the C-H acid to the nitrophenide anion and subsequent formation of the σ-adduct by the reaction of 1,3-dinitrobenzene with the carbanion within the ion-molecule complex. It was found that such a reaction is possible only for C-H acids with a gas-phase acidity lying within a narrow, strictly defined range whose location on the acidity scale depends on the acidity of the nitroarene. The σ-adduct formed in the reaction of the 2,4-dinitrophenide anion with CH2Cl2 undergoes rapid HCl elimination yielding an anion with the same composition as that produced by the Vicarious Nucleophilic Substitution of hydrogen reaction but with a different structure. [Copyright &y& Elsevier]

Isoprene (C 5 H 8 ) is the main non-methane hydrocarbon emitted into the global atmosphere. Despite intense research, atmospheric transformations of isoprene leading to secondary organic aerosol (SOA) are still not fully understood, including its multiphase chemical reactions. Herein, we report on the detailed structural characterization of atmospherically relevant isoprene-derived organosulfates (OSs) with a molecular weight (MW) of 212 (C 5 H 8 SO 7 ), which are abundantly present in both ambient fine aerosol (PM 2.5 ) and laboratory-generated isoprene SOA. The results obtained from smog chamber-generated isoprene SOA and aqueous-phase laboratory experiments coupled to the S(IV)-autooxidation chemistry of isoprene, 3-methyl-2(5 H )-furanone, and 4-methyl-2(5 H )-furanone, allowed us for the first time to fully elucidate the isomeric structures of the MW 212 OSs. By applying liquid chromatography interfaced to electrospray ionization high-resolution mass spectrometry, we firmly confirmed six positional isomers of the MW 212 OSs in PM 2.5 collected from different sites in Europe and the United States. Our results also show that despite the low solubility of isoprene in water, aqueous-phase or multiphase chemistry can play an important role in the formation of OSs from isoprene. Possible formation mechanisms for the MW 212 OSs are also tentatively proposed.