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The presence of steric hindrance triggers different reaction pathways in the intramolecular oxidative aromatic coupling of tetraaryl-pyrrolo[3,2-b]pyrroles and leads to the formation of a fluorene moiety and a new cationic π-system linked together by a spiro carbon atom. Computational studies elegantly rationalized these results. These previously unknown functional dyes emit red light with reasonable efficiency. [ABSTRACT FROM AUTHOR]

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]

Reactions of aromatic and heteroaromatic compounds involving anions are of great importance in organic synthesis. Some of these reactions have been studied in the gas phase and are occasionally mentioned in reviews devoted to gas-phase negative ion chemistry, but no reviews exist that collect all existing information about these reactions. This work is intended tofill this gap. In the first part of this review, methods for generating arene anions in the gas phase and studying their physicochemical properties and fragmentation reactions are presented. The main topics in this part are as follows: processes in which gasphase arene anions are formed, measurements and calculations of the proton affinities of arene anions, proton exchange reactions, and fragmentation processes of substituted arene anions, especially phenide ions. The second part is devoted to gas-phase reactions of arene anions. The most important of these are reactions with electrophiles such as carbonyl compounds and a,b-unsaturated carbonyl and related compounds (Michael acceptors). Other reactions including oxidation of arene anions and halogenophilic reactions are also presented. In the last part of the review, reactions of electrophilic arenes with nucleophiles are discussed. The best known of these is the aromatic nucleophilic substitution (SNAr) reaction; however, other processes that lead to the substitution of a hydrogen atom in the aromatic ring are also very important. Aromatic substrates in these reactions are usually but not always nitroarenes bearing other substituents in the ring. The first step in these reactions is the formation of an anionic s-adduct, which, depending on the substituents in the aromatic ring and the structure of the attacking nucleophile, is either an intermediate or a transition state in the reaction path. In the present review, we attempted to collect the results of both experimental and computational studies of the aforementioned reactions conducted since the very beginning of gas-phase negative ion chemistry. [ABSTRACT FROM AUTHOR]

It has been found that anionic σ-adducts formed in the reactions of highly electrophilic nitroarenes with selected carbanions, alkoxide anions and amines can be transferred to the gas phase using an electrospray ion source and the resulting ions can be studied using various mass spectrometry techniques in the solvent-free environment. This method can also be used for estimating the relative equilibrium constants of the σ-adduct formation reactions in a liquid phase. [Copyright &y& Elsevier]

In this study, we present a complete description of the addition of a model nucleophile to the nitroaromatic ring in positions occupied either by hydrogen (the first step of the SNAr-H reaction) or a leaving group (SNAr-X reaction) using theoretical parameters including aromaticity (HOMA), electrophilicity and nucleophilicity indices. It was shown both experimentally and by our calculations, including kinetic isotope effect modeling, that the addition of a nucleophile to the electron-deficient aromatic ring is the rate limiting step of both SNAr-X and SNAr-H reactions when the fast transformation of σH-adduct into the products is possible due to the specific reaction conditions, so this is the most important step of the entire reaction. The results described in this paper are helpful for better understanding of the subtle factors controlling the reaction direction and rate. [ABSTRACT FROM AUTHOR]

Highlights: [•] Proton affinity of 65 aromatic acids has been measured by Cooks’ kinetic method. [•] For all but one acid the simplified kinetic method can be used. [•] For salicylic acid it is necessary to introduce entropy correction. [•] The results for dinitrobenzoic acids should be corrected for further fragmentation. [ABSTRACT FROM AUTHOR]