Aromatic compounds heterocycles

Further exploitation of the molecular shape feature has led more recently to the design of another series of clathrate hosts by substituting on the allene rigid backbone bulky groups 22>, Representative compounds of this new host family are 20 and 21. The allene 20 (R = t-butyl) shows an interesting clathration behaviour upon crystallization from various environments, including alicyclic and aromatic compounds, heterocycles, cyclic ketones and eyclohexaneamine 26>. 

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. 

After this introductory Chapter 1, Chapter 2 provides a proper chemical introduction to the phenomenon of chirality and to the polarimetric and spectroscopic methods of its assessment. First, the authors discuss structural asymmetry of the compounds in general terms and also a variety of structural preconditions for its appearance. Then they focus in greater detail on different classes of organic compounds, such as alkanes and cycloalkanes, alkenes, aromatic compounds, heterocyclic compounds, other compounds containing heteroatoms, and complexes. 

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... 

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

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

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. 

Cyclic compounds that contain at least one atom other than carbon within their ring are called heterocyclic compounds, and those that possess aromatic stability are called het erocyclic aromatic compounds Some representative heterocyclic aromatic compounds are pyridine pyrrole furan and thiophene The structures and the lUPAC numbering system used m naming their derivatives are shown In their stability and chemical behav lor all these compounds resemble benzene more than they resemble alkenes... 

Heterocyclic aromatic compounds can be polycyclic as well A benzene ring and a pyridine ring for example can share a common side m two different ways One way gives a compound called quinoline the other gives isoquinoline... 

A large group of heterocyclic aromatic compounds are related to pyrrole by replacement of one of the ring carbons p to nitrogen by a second heteroatom Com pounds of this type are called azoles... 

The structural types described m this section are but a tiny fraction of those pos sible The chemistry of heterocyclic aromatic compounds is a nch and varied held with numerous applications... 

Section 11 22 Heterocyclic aromatic compounds are compounds that contain at least one atom other than carbon within an aromatic ring... 

Section 11 23 Huckel s rule can be extended to heterocyclic aromatic compounds Unshared electron pairs of the heteroatom may be used as tt electrons as necessary to satisfy the 4n + 2 rule... 

Acridine is a heterocyclic aromatic compound obtained from coal tar that is used in the syn thesis of dyes The molecular formula of acndine is C13H9N and its ring system is analogous to that of anthracene except that one CH group has been replaced by N The two most stable reso nance structures of acridine are equivalent to each other and both contain a pyndine like struc tural unit Wnte a structural formula for acridine... 

Section 12 18 Heterocyclic aromatic compounds may be more reactive or less reactive than benzene Pyridine is much less reactive than benzene but pyrrole furan and thiophene are more reactive... 

Halides derived from certain heterocyclic aromatic compounds are often quite reac tive toward nucleophiles 2 Chloropyridme for example reacts with sodium methoxide some 230 million times faster than chlorobenzene at 50°C... 

Nucleic acids are acidic substances present m the nuclei of cells and were known long before anyone suspected they were the primary substances involved m the storage transmission and processing of genetic information There are two kinds of nucleic acids ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) Both are complicated biopolymers based on three structural units a carbohydrate a phosphate ester linkage between carbohydrates and a heterocyclic aromatic compound The heterocyclic aro matic compounds are referred to as purine and pyrimidine bases We 11 begin with them and follow the structural thread... 

Two nitrogen containing heterocyclic aromatic compounds—pyrimidine and purine— are the parents of the bases that constitute a key structural unit of nucleic acids... 

Section 28 1 Many biologically important compounds are related to the heterocyclic aromatic compounds pyrimidine and purine... 

Carbocyclic compounds are very usefully divided into (a) saturated (alicyclic) compounds, (b) aromatic compounds and (c) the intermediate partially unsaturated (alicyclic) compounds. Heterocyclic compounds can be subdivided in exactly the same way, and equally usefully. 

The numerical value of hardness obtained by MNDO-level calculations correlates with the stability of aromatic compounds. The correlation can be extended to a wider range of compounds, including heterocyclic compounds, when hardness is determined experimentally on the basis of molar reffactivity. The relatively large HOMO-LUMO gap also indicates the absence of relatively high-energy, reactive electrons, in agreement with the reduced reactivity of aromatic compounds toward electrophilic reagents. 

Ultraviolet The determination of organic compounds, expecially aromatic and heterocyclic substances or compounds with conjugated bonds. ... 

Yagupol skii, L M Aromatic and Heterocyclic Compounds with Fluorine Containing Suhsniuenis (Russ ) Naukova Dumka Kiev USSR 320... 

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