Condensed ring systems

Many biologically important heterocyclic compounds have fused (condensed) ring systems. In particular, the purines adenine and guanine are found in DNA (with cytosine, 5-methylcytosine, and thymine) and also in RNA (with cytosine and uracil). 

Problem 20.36 Which dicarboxylic acid is formed on oxidation of quinoline The pyridine ring is more stable than the benzene ring [Problem 20.19(ft)J. 

Problem 20.37 Ouinoline is prepared by the Skraup reaction of aniline, glycerol and nitrobenzene. Suggest a mechanism involving Michael addition of aniline to an a,)3-unsaturated aldehyde, ring closure, and then dehydration and oxidation. 

Problem 20.38 Give the expected products of (a) monobromination of quinoline, b) catalytic reduction of quinoline with 2mol of H,. M 

Problem 20.39 Give structures for the products of reaction of quinoline with (n) HNO,. H,SO (b) NaNH  

There can be but few closely related pairs of isomers like 1,2- and 

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Many chemical compounds have been described in the Hterature as fluorescent, and since the 1950s intensive research has yielded many fluorescent compounds that provide a suitable whitening effect however, only a small number of these compounds have found practical uses. Collectively these materials are aromatic or heterocycHc compounds many of them contain condensed ring systems. An important feature of these compounds is the presence of an unintermpted chain of conjugated double bonds, the number of which is dependent on substituents as well as the planarity of the fluorescent part of the molecule. Almost all of these compounds ate derivatives of stilbene [588-59-0] or 4,4 -diaminostilbene biphenyl 5-membeted heterocycles such as triazoles, oxazoles, imidazoles, etc or 6-membeted heterocycles, eg, coumarins, naphthaUmide, t-triazine, etc. 

The anthraquiaone vat dyes can be classified into several groups on the basis of their chemical stmctures (/) benzanthrone dyes, (2) indanthrones, (3) anthrimides, (4) anthrimidocarbazoles, (5) acylaminoanthraquinones, (6) anthraquinoneazoles, (7) anthraquiaone acridones, (8) anthrapyrimidines, and 9) highly condensed ring systems. Most currendy (1993) available dyes have been known for many decades, and very few new dyes have been commercialized since the 1970s. Recendy, research and development efforts have focused on improved manufacturing of traditional vat dyes. 

Various reviews dealing with the 1,2.4-triazines have been published. The most recent is that published by Neunhoeffer and Wiley (78HC749) covering the literature through 1974. Owing to the increase of the number of publications on the 1,2,4-triazines, a survey of the literature on their condensed ring systems with three- to five-membered heterocycles, from 1974 through 1992, constitutes the subject of this review. 

In the case of the aromatic hydrocarbons with condensed ring systems the state of affairs is quite similar. Thus the following structures have been proposed for naphthalene ... 

Naphthalene, anthracene, and other condensed ring systems... 

It may be mentioned that in heterocyclic systems as well as in hydrocarbon condensed ring systems the contribution to the normal state of structures associated with all of the possible positions of the double bonds is dependent on the existence of a coplanar arrangement of the per-tinent atoms, with bond angles of about 120°, which requires that the rings contain five or six or possibly seven atoms. 

If reaction (13) is carried out under H2 in the absence of capping agent then oligomers with Mjj 2000 D can be isolated following distillation of the volatile cyclomers. We believe that in this case the product polymers are both condensed ring systems and hydrogen capped linear oligomers. 

Tabulated Data on Density - Condensed Ring Systems... 

Figure 12.5 Cholesterol ester. Cholesterol is a derivative of the cyclopentanoper-hydrophenanthrene condensed ring system and is therefore a member of the group of compounds called steroids. It often occurs esterified at position 3 with a long chain fatty acid, which may be saturated or unsaturated and commonly contains 16 or 18 carbon atoms. Steroids that form esters in this way are more correctly called sterols.

Table 12 shows the cis effect of the axial ligand X or L on the optical spectrum of cobalt(III) etioporphyrin derivatives Co(Etio-I)LX [32a-h] which behave similarly to the corresponding rhodium(III) complexes (Table 4). Analogous trends are found in the Co(TTP)LX series (133). The only notable feature is the large bathochromic shift caused by benzimidazole in [32h] obviously this ligand is far more different from pyridine than imidazole, the condensed ring system acting as a stronger 7r-acceptor.

Aromatic hydrocarbon a hydrocarbon characterized by the presence of an aromatic ring or condensed aromatic rings benzene and substituted benzene, naphthalene and substituted naphthalene, phenan-threne and substituted phenan-threne, as well as the higher condensed ring systems compounds that are distinct from those of aliphatic compounds (q.v.) or ali-cyclic compounds (q.v.). 

The introduction of further ring nitrogen atoms into [98] usually does not chauige the site of protonation, which remains N-1 (Armarego, 1965). The condensed ring system [99], however, adds... 

Aptotic solvents can be used for the reduction of aromatic hydrocarbons, particularly the condensed ring systems. Solvents used for the conversion of benzene to cyclohexa-1,4-diene at a mercury cathode under constant current conditions include dimethoxyethanc [45] and N-medtylpyrrolidone [46]. Each solvent contained water as a proton source and tetraethylammonium bromide as supporting electro-... 

Condensed ring systems, in polysulfidemetal complexes, 31 101-102 Conductance measurements, of halogen complexes, 3 104... 

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