Heteroaromatic compounds structures

The Formation of Anionic cr-Adducts from Heteroaromatic Compounds Structures, Rates, and Equilibria... 

Illuminati, G., Stegel, F., The Formation of Anionic a-Adducts from Heteroaromatic Compounds Structures, Rates, and Equilibria, 34, 30S. lonescu, M., Mantsch, H., Phenoxazines, 8,83. 

Nucleophilic heteroaromatic substitution , Illuminati, G., Adv. Heterocycl. Chem., 1964, 3, 285 Reactivity of azine, benzoazine, and azinoazine derivatives widi simple nucleophiles . Shepherd, R. G. and Fedrick, J. L., ibid., 1965, 4, 145 Formation of anionic a-adducts from heteroaromatic compounds structures, rates and equilibria , Illuminati, G. and Stegel, F, ibid., 1983, 34, 306. 

The classical structures of pyrrole, furan and thiophene (31) suggest that these compounds might show chemical reactions similar to those of amines, ethers and thioethers (32) respectively. On this basis, the initial attack of the electrophile would be expected to take place at the heteroatom and lead to products such as quaternary ammonium and oxonium salts, sulfoxides and sulfones. Products of this type from the heteroaromatic compounds under consideration are relatively rare. 

Hetero[13]annulene, bis-dehydro-dimethylated structure, 7, 716 H etero[ 17]annulenes H NMR, 7, 719, 721 restricted structure, 7, 720 Heteroaromatic compounds reactions... 

Structure elucidation does not necessarily require the complete analysis of all multiplets in complicated spectra. If the coupling constants are known, the characteristic fine structure of the single multiplet almost always leads to identification of a molecular fragment and, in the case of alkenes and aromatic or heteroaromatic compounds, it may even lead to the elucidation of the complete substitution pattern. 

The heteroaromatic compounds can be divided into two broad groups, called n-excessive and n-deficient, depending on whether the heteroatom acts as an electron donor or an electron acceptor. Furan, pyrrole, thiophene, and other heterocyclics incorporating an oxygen, nitrogen, or sulfur atom that contributes two n electrons are in the rr-exeessive group. This classification is suggested by resonance structures and confirmed by various MO methods. ... 

Bromine titration has been applied to several heteroaromatic compounds, but it is not a reliable method. The assumption is often made that oxo structures react very slowly with bromine whereas the hydroxy forms react rapidly. Thus, 3,4-diphenylisoxazol-5-one when freshly dissolved in ethanol was found to react with 0.5 mole of bromine, but after standing it reacted with almost 1 mole. These observations led to the conclusion that the solid was in the CH... 

Reactions of uracil and structurally analogous compounds have been thoroughly studied 49, 50). Uracil (2,4-dihydroxypyrimidine), a component of the nucleic acids, can be classified as a heteroaromatic compound only with reserve, sinee the keto form dominates in the tautomeric equilibrium. 

Two chapters in this volume describe the generation of carbocations and the characterization of their structure and reactivity in strikingly different milieu. The study of the reactions in water of persistent carbocations generated from aromatic and heteroaromatic compounds has long provided useful models for the reactions of DNA with reactive electrophiles. The chapter by Laali and Borosky on the formation of stable carbocations and onium ions in water describes correlations between structure-reactivity relationships, obtained from wholly chemical studies on these carbocations, and the carcinogenic potency of these carbocations. The landmark studies to characterize reactive carbocations under stable superacidic conditions led to the award of the 1994 Nobel Prize in Chemistry to George Olah. The chapter by Reddy and Prakash describes the creative extension of this earlier work to the study of extremely unstable carbodications under conditions where they show long lifetimes. The chapter provides a lucid description of modern experimental methods to characterize these unusual reactive intermediates and of ab initio calculations to model the results of experimental work. 

Aza and polyaza heteroaromatic compounds generally undergo C-attachment of the amide ion in KNH2-NH3. The structure of the resulting a-adducts has been firmly established in a large number of instances. 

Electronic Structures of Some Heteroaromatic Compounds Yuki Gosei Kagaku Kyokai Shi, 1972, 30, 217-227. 

The study of the reactivity of the nucleic acid bases utilizes indices based on the knowledge of the molecular electronic structure. There are two possible approaches to the prediction of the chemical properties of a molecule, the isolated and reacting-molecule models (or static and dynamic ones, respectively). Frequently, at least in the older publications, the chemical reactivity indices for heteroaromatic compounds were calculated in the -electron approximation, but in principle there is no difficulty to define similar quantities in the all-valence or allelectron methods. The subject is a very broad one, and we shall here mention only a new approach to chemical reactivity based on non-empirical calculations, namely the so-called molecular isopotential maps. 

Volume 72 of Advances in Heterocyclic Chemistry consists of six chapters. The first considers the role of five- and six-membered heteroaromatic compounds as ct and ir ligands. Authored by Professors A. D. Garnovskii (Rostov-on-Don, Russia) and A. P. Sadimenko (Fort Hare, South Africa), it gives an overview of the multitude of structural types that can arise when heterocycles are used as ligands in organometallic derivatives. Many such compounds are of great industrial importance in catalytic and other processes. No previous comprehensive overview of this subject has been available. 

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