Heterocyclic compounds aromatic heterocycles

This reagent affords compounds (1 1) with aromatic hydrocarbons and other classes of organic compounds (heterocyclic compounds, aromatic ethers, etc.). 

Aromaticity has been long recognized as one of the most useful theoretical concepts in organic chemistry. It is essential in understanding the reactivity, structure and many physico-chemical characteristics of heterocyclic compounds. Aromaticity can be defined as a measure of the basic state of cyclic conjugated TT-electron systems, which is manifested in increased thermodynamic stability, planar geometry with non-localized cyclic bonds, and the ability to sustain an induced ring current. In contrast to aromatic compounds there exist nonaromatic and antiaromatic systems. Thus, pyrazine (69)... 

The chart in Fig. 99 concerns liquid cyclic compounds (aromatic, hydroaromatic, heterocyclic). In this graph, the curve B limits the area characterizing liquids that produce solutions of relatively low viscosity while the area C again defines liquids that cause swelling only. 

Alkenes, alkynes, aromatic compounds, aromatic heterocyclic, highly conjugated aliphatics such as carotenes 200-500 10 -10 ... 

This chapter consists of four sections viz Aliphatic Compounds, Alicyclic Compounds, Aromatic Compounds and Heterocyclic Compounds. 

Crude and refined oils are known to contain the following aromatic compounds aromatic and polynuclear aromatic hydrocarbons (PAHs), phenols and cresols, heterocyclics (such as pyridine, quinoline), benzoic acid, esters and ethers. Many are quite water-soluble (Table IV) and are expected to be found in the dissolved fraction. 

This chapter consists of five sections viz Aliphatic Compounds, Alicyclic Compounds, Aromatic Compounds, Heterocyclic Compounds and MisceUaneous As, B, P, Si, S, Se, and Te Compounds. 

In addition, liver preparations from rats induced with Aroclor 1254 (Monsanto) showed the best general applicability for activation. However, individual differences in effectiveness do occure.g., in the results given in Table 5, variously induced preparations show obvious differences between fraction 9 (the basic fraction. Be) and fraction 14 (the neutral/methanol fraction). The Aroclor-induced preparation works best with the neutral fraction (PAHs ), whereas the phenobarbital-induced preparations work more efficiently with the basic fraction (heterocyclic nitrogen compounds, aromatic amines, aza-arenes ). 

The aromatic extracts are black materials, composed essentially of condensed polynuclear aromatics and of heterocyclic nitrogen and/or sulfur compounds. Because of this highly aromatic structure, the extracts have good solvent power. 

Decolorisation by Animal Charcoal. It sometimes hap pens (particularly with aromatic and heterocyclic compounds) that a crude product may contain a coloured impurity, which on recrystallisation dissolves in the boiling solvent, but is then partly occluded by crystals as they form and grow in the cooling solution. Sometimes a very tenacious occlusion may thus occur, and repeated and very wasteful recrystallisation may be necessary to eliminate the impurity. Moreover, the amount of the impurity present may be so small that the melting-point and analytical values of the compound are not sensibly affected, yet the appearance of the sample is ruined. Such impurities can usually be readily removed by boiling the substance in solution with a small quantity of finely powdered animal charcoal for a short time, and then filtering the solution while hot. The animal charcoal adsorbs the coloured impurity, and the filtrate is usually almost free from extraneous colour and deposits therefore pure crystals. This decolorisation by animal charcoal occurs most readily in aqueous solution, but can be performed in almost any organic solvent. Care should be taken not to use an excessive quantity... 

Retro-Synthetic Analysis (= Antithesis 193 3.1.5 Aromatic and Heterocyclic Compounds... 

Typical nucleophiles known to react with coordinated alkenes are water, alcohols, carboxylic acids, ammonia, amines, enamines, and active methylene compounds 11.12]. The intramolecular version is particularly useful for syntheses of various heterocyclic compounds[l 3,14]. CO and aromatics also react with alkenes. The oxidation reactions of alkenes can be classified further based on these attacking species. Under certain conditions, especially in the presence of bases, the rr-alkene complex 4 is converted into the 7r-allylic complex 5. Various stoichiometric reactions of alkenes via 7r-allylic complex 5 are treated in Section 4. 

The cross-coupling of aromatic and heteroaromatic rings has been carried out extensively[555]. Tin compounds of heterocycles such as oxazo-lines[556,557], thiophene[558,559], furans[558], pyridines[558], and seleno-phenes [560] can be coupled with aryl halides. The syntheses of the phenylo.xazoline 691[552], dithiophenopyridine 692[56l] and 3-(2-pyridyl)qui-noline 693[562] are typical examples. 

Indole is classified as a 7c-excessive aromatic compound. It is isoelectronic with naphthalene, with the heterocyclic nitrogen atom donating twm of the ten 7t-electrons. 

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