Chemical benzene ring aryl group

Dimethylbenzene has two types of protons those attached directly to the benzene ring and those of the methyl groups. Aryl protons are significandy less shielded than alkyl protons. As shown in text Table 13.1 they are expected to give signals in the chemical shift range 8 6.5-8.5 ppm. Thus, the... [Pg.320]

The chemistry of benzene and its derivatives is quite different from that of alkenes and alkynes, but even though we do not study the chemistry of arenes until Chapters 21 and 22, we will show structural formulas of compounds containing aryl groups before then. The three double bonds in a six-membered ring create a special stabilization called aromaticity, which lowers the reactivity of benzene relative to other alkenes. What you need to remember at this point is that an aryl group is not chemically reactive under any of the conditions we describe in Chapters 6 through 20. [Pg.224]

By contrast, poly(phen)denes) are stable to chemical oxidation owing to their inactive benzene rings. However, they have poor flexibility because of the inherent rigidness of all-benzene ring architectures. Poly(aryl benzimidazoles) and poly(aryl imides) have also been used as polymer matrices in HEMs. Their biggest issue is poor chemical stability, because the benzimidazole and imide groups have been confirmed to hydrolyze irreversibly in alkaline media under certain conditions. Besides, poly(aryl benzimidazoles) also have very limited solubility in common solvents, rendering chemical modification difficult... [Pg.161]

The effects of the 1,2,3-triazole and 1-amino-1,2,3-triazole heterocycles on the chemical shift of the carbon atoms in the phenyl ring of compounds (40) and (41) (X = H) are compared with the value for benzene. With regard to the effects of substituent X para and meta) on the 1,2,3-triazole carbons, C(4) is deshielded by electron-withdrawing groups, whereas C(5) is shielded. Reasonable correlations with Hammett a values are observed for the chemical shifts of both C(4) and C(5) of (41) <86MRC53>. The chemical shifts of C(4) and C(5) in 5-amino-l-aryl-l,2,3-triazoles are shifted upheld by 2-5 ppm compared with the corresponding 5-anilino-1,2,3-triazoles. In 5-anilino-... [Pg.14]

The chemical reactivity of the thiocyano groups in these chelate rings has not been investigated, but the halogen atoms in the 3-halo metal acetylacetonates have been found to be quite inert and their behavior is different from that of aryl halides, since treatment of the tris(3-bromo-2,4-pentanediono)chromium(III) chelate with magnesium or lithium in benzene or tetrahydrofuran resulted in no reaction. Attempted nucleophilic displacement of the bromine atoms in this chelate by azide, acetate, nitrate, and iodide ions in hot dimethylformamide also failed. In most of these... [Pg.191]

CHAllENCEl Biochemical oxidation of aromatic rings is catalyzed by a group of liver enzymes called aryl hydroxylases. Part of this chemical process is the conversion of toxic aromatic hydrocarbons such as benzene into water-soluble phenols, which can be easily excreted. However, the primary purpose of the enzyme is to enable the synthesis of biologically useful compounds, such as the amino acid tyrosine from its relative phenylalanine (below). [Pg.1034]

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