Condensed-ring aromatics

Aromatic condensed rings are of cata-condensed type. 

In the early studies, the phosphine oxides resolved contained substituents with aromatic condensed rings (entries 2 and 3) but later other oxides without that substitution were also resolved (entries 1 and 5) and even secondary phosphine oxides (entry 7). Entries 8-15 show some resolutions of the phosphine boranes including examples with several stereogenic centres in the backbone (entries 11-14). Compound of entry 11 can be regarded as a hybrid between BPE and DiPAMP. A few diastereomeric pairs have also been resolved by HPLC (entries 16 and 17), because conventional methods such as column chromatography or recrystallisation failed. 

Part 28. Other Chromophores consisting of 2 carbo-aromatic condensed Rings... 

Polynuclear, aromatic, condensed-ring compounds absorb in the same general regions as benzene derivatives " and therefore the previous section should be noted carefully. (A study of pyrenes has been published. )... 

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. 

Coal tar is the condensation product obtained by cooling to approximately ambient temperature, the gas evolved in the destmctive distillation of coal. It is a black viscous Hquid denser than water and composed primarily of a complex mixture of condensed ring aromatic hydrocarbons. It may contain phenoHc compounds, aromatic nitrogen bases and their alkyl derivatives, and paraffinic and olefinic hydrocarbons. Coal-tar pitch is the residue from the distillation of coal tar. It is a black soHd having a softening point of 30—180°C (86—359°F). 

Catalysts in this service can deactivate by several different mechanisms, but deactivation is ordinarily and primarily the result of deposition of carbonaceous materials onto the catalyst surface during hydrocarbon charge-stock processing at elevated temperature. This deposit of highly dehydrogenated polymers or polynuclear-condensed ring aromatics is called coke. The deposition of coke on the catalyst results in substantial deterioration in catalyst performance. The catalyst activity, or its abiUty to convert reactants, is adversely affected by this coke deposition, and the catalyst is referred to as spent. The coke deposits on spent reforming catalyst may exceed 20 wt %. 

Another class of compounds is called condensed-ring or fused-ring systems. These structures contain two or more aromatic rings that share a pair of carbon atoms. Examples include naphthalene, anthracene, and phenanthrene, the latter two being isomeric structures. 

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 ... 

The six-membered aromatic A ring originates from three units of malonyl-CoA, produced from citrate precursors through the activity of a cytosolic acetyl-CoA carboxylase (ACC) (Fatland and others 2004) (see Fig. 5.1). These three malonyl-CoA units are added through sequential decarboxylation condensation reactions and actually represent the first committed step toward flavonoid biosynthesis. 

Unsubstituted aromatic PAHs with fewer than 4 condensed rings have not shown tumorigenic... 

The amidine group reacted more easily than the aromatic amino group with EMME in boiling ethanol besides the condensation, ring closure usually takes place to give pyrimidinecarboxylate in good yield (e.g., 80EUP15772) (Scheme 11). 

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.). 

Finally, indole ring formation is via condensation of the amino and keto functions. This is analogous to imine formation, as seen in part (a), but dehydration produces the aromatic pyrrole ring rather than an imine. Alternatively, one could write imine formation followed by tautomerism to the aromatic enamine. 

---