Chemical benzene ring aryl

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... 

By what chemical reactions can a halogen in a benzene ring be replaced by (o) OH, (6) alkyl radical, (c) aryl radical, id) COOH, (e) H ... 

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... 

Chemical/Physical. Under atmospheric conditions, the gas-phase reaction of o-xylene with OH radicals and nitrogen oxides resulted in the formation of o-tolualdehyde, o-methylbenzyl nitrate, nitro-o-xylenes, 2,3-and 3,4-dimethylphenol (Atkinson, 1990). Kanno et al. (1982) studied the aqueous reaction of o-xylene and other aromatic hydrocarbons (benzene, toluene, w and p-xylene, and naphthalene) with hypochlorous acid in the presence of ammonium ion. They reported that the aromatic ring was not chlorinated as expected but was cleaved by chloramine forming cyanogen chloride. The amount of cyanogen chloride formed increased at lower pHs (Kanno et al., 1982). In the gas phase, o-xylene reacted with nitrate radicals in purified air forming the following products 5-nitro-2-methyltoluene and 6-nitro-2-methyltoluene, o-methylbenzaldehyde, and an aryl nitrate (Chiodini et ah, 1993). 

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-... 

Free radical attack at the pyridine ring is noted for its low selectivity and substituents have little effect. Arylation takes place at all three positions, but halogen atoms preferentially attack the a-, and alkyl radicals the a- and y-positions. Metals such as sodium and zinc transfer a single electron to pyridine to form anion radicals. These can dimerize by reaction at the a- or y-position to yield dipyridyls by loss of hydride ion. Thus, reduction of pyridine by chemical and catalytic means is easier than reduction of benzene. 

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