Aromatic ring condensation

The 6-benzofuranylaminomethylenemalonate (928) can be regarded as both a /we/o-alkoxy-substituted and an aromatic ring condensed phenyla-mine derivative. On thermal ring closure in boiling Dowtherm A for 30 min, a 1 1 mixture of furo[3,2-g]quinoline-6-carboxylate (929) and furo [2,3-/]quinoline-8-carboxylate (930) was obtained in 70-80% yield (70GEP2021100 71BRP1240446), indicating that both the alkoxy substituted and the aromatic moiety exerted an influence. 

Other researchers have reported that the cyclization step is believed to be rate determining in the cycloaromatization (Bergman) reaction of aliphatic enediynes." It has been found that the rate-limiting step is hydrogen abstraction by benzannelation. This effect should be attributable to the faster rate of retro-Bergman cyclization from the aromatic ring-condensed 1,4-didehydrobenzene diradicals and/or the slower rate of hydrogen abstraction by them. 

Other reactions leading to NH4 removal from soil solution besides microbial nitrogen assimilation, metal-ammine formation, or adsorption onto mineral surfaces, involve NH3 fixation by incorporating it as NH2 in aromatic rings of humic acids (quinone) followed with aromatic ring condensation. 

The percentage of aromatic carbon can be determined now by solid state NMR. Extensive work in this area is reported in the literature (2, 4, 5). The other two questions cannot be answered definitively by solid state studies alone. One should mention the work of Friedel and Queiser (6) in which information on the degree of aromatic ring condensation was obtained by UV-visible spectroscopy on coal itself. They concluded that the degree of aromatic ring condensation is quite low in bituminous coals. 

When the acetylenic groups are in the para positions on the aromatic ring, condensation with a metal phosphine leads to a linear polymer as in (8.358), but if these groups are in the ortho position a cyclic tetrameric ring is produced as in (8.357) [33]. With three pendant acetylenic groups, dendritic-type structures can be obtained as in (8.356). 

Professor Claris considered by many scientists to be the father of modem polycyclic aromatic hydrocarbon chemistry. His most Important contributions to polycyclic aromatic hydrocarbon chemistry were the discovery of the anellatlon principle (Aromatic ring condensation), his pi sextet theory of PAH, the development of ben zogenic diene synthesis known as the Clar reaction, the synthesis of numerous new PAH systems, and classification of UV absorption bands of PAH corresponding to alpha, beta, and para bands. 

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