Parent aromatic compounds

The H NMR spectra of the parent heterocycles (Table 4) each consist of two multiplets, of which the one at lower field is assigned to the a-hydrogens. 

Apart from pyrrole, the chemical shifts for the [3-protons increase with decreasing electronegativity of the heteroatom. In contrast, the chemical shifts of the a-protons do not display any obvious regularity, probably due to paramagnetic shielding contributions which will become more important with increasing availability of 7-orbitals. The chemical shift of the pyrrole N-H is solvent dependent. 

The ring proton chemical shifts of 2H-pyrroles and 3H-pyrroles are as expected for conjugated imines (B-90MI201-02). 

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Many aromatic compounds are simply substituted derivatives of benzene and are named accordingly Many others have names based on some other parent aromatic compound... 

Sulfonic acids are prone to reduction with iodine [7553-56-2] in the presence of triphenylphosphine [603-35-0] to produce the corresponding iodides. This type of reduction is also facile with alkyl sulfonates (16). Aromatic sulfonic acids may also be reduced electrochemicaHy to give the parent arene. However, sulfonic acids, when reduced with iodine and phosphoms [7723-14-0] produce thiols (qv). Amination of sulfonates has also been reported, in which the carbon—sulfur bond is cleaved (17). Ortho-Hthiation of sulfonic acid lithium salts has proven to be a useful technique for organic syntheses, but has Httie commercial importance. Optically active sulfonates have been used in asymmetric syntheses to selectively O-alkylate alcohols and phenols, typically on a laboratory scale. Aromatic sulfonates are cleaved, ie, desulfonated, by uv radiation to give the parent aromatic compound and a coupling product of the aromatic compound, as shown, where Ar represents an aryl group (18). 

Griess (1860) coined the prefix diazo for the nitrosation product of an aromatic amine, because he assumed that two nitrogen atoms replaced two hydrogen atoms of the parent aromatic compound. On the other hand, azobenzene received its name on the basis of the C H N ratio 6 5 1, indicating the replacement of one hydrogen by one nitrogen atom. 

Aromatic systems are named in a similar way, but additional stem names need to be used. Parent aromatic compounds of importance are benzene. 

The composition of anthracene oil is dominated by parent aromatic compounds possessing 2, 3, and 4 aromatic rings. 

The radical anion can participate in electron transfer reactions, in which the electron is transferred to a compound with suitable electron affinity. The parent aromatic compound is regenerated. Such a reaction is shown in Eq. (83), where chlorobenzene is dechlorinated by electron transfer from the benzene radical anion ... 

Attempts have been made to correlate displacements of the absorption bands of parent aromatic compounds by substituents with Hammett a-values derived from the effects of the substituents on ground state kinetic and equilibrium properties. For example,... 

Parent aromatic compound Ring retained products Ring fragmented products... 

Thiiranes derived from aromatic hydrocarbons are thermally labile. For example, phenanthrene episulfide 10 was detected spectrometrically at —55 °C but was too unstable to isolate <2000JOC8083>. It decomposed spontaneously to elemental sulfur even at 0°C, thus restoring the parent aromatic compound (Scheme 10). The relative stability of various arene episulfides has been calculated and in general they are much less thermodynamically stable than the corresponding epoxide <1998T14283>. 

Altered Aromatic Metabolites. Loss of parent compound is insufficient evidence to support the occurrence of biodegradation. Frequently, the disappearance of the parent aromatic compound results in the formation of an altered aromatic metabolite. This product indicates that, although biotransformation has taken place, biodegradation has not. An example is the anaerobic O-demethylation of chlorinated guaiacols to chlorocatechols mediated by the acetogenic bacteria, Acetobacterium woodii and Eubacterium limosum (37). 

Fluorescence and GC/MS analyses show Chat carbonized coal hydrocarbons are widespread contaminants of sediments In the Elizabeth River, Norfolk, Va. The highest levels are found In the vicinity of suspected sources and generally decrease with Increased distance from these sources. Parent aromatic compounds are the predominant hydrocarbon component of carbonized coal and can be uniquely detected even In the presence of petroleum hydrocarbons. Carbonized coal products are a chronic source of priority pollutant polynuclear aromatic hydrocarbons in the Elizabeth River. 

Lloyd and McNab investigated the behavior of 1,2-dihydropyrimidinium salts in reactions with different electrophilic and nucelophilic reagents and concluded that these dihydropyrimidinium compounds present an intriguing example of dihydro aromatic compounds, which show much greater reactivity toward electrophilic substitution than do the parent aromatic compounds.161... 

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