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Benzene, Aromaticity, and Benzene Derivatives
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
This question can be answered by the nitration reaction of pyrrole with nitric acid/acetic anhydride. Note that nitric acid reacts with acetic anhydride to give the nitronium ion, NO2+, which is the nitrating agent. Pyrrole is much more reactive and requires a milder nitration reagent relative to benzene. Reaction at C2 generates arenium ion A, with a very stable iminium ion resonance contributor. Reactions at C3 gives B, and also has a very stable iminium ion resonance contributor. These very stable iminium ions are, arguably, a significant reason why pyrrole is considered to be more activated than benzene. The ability to form stable arenium ions contributes to the electron-donating ability of pyrrole in SEAr reactions, making pyrrole very reactive and activated. Note that reaction at C2 generates an arenium ion with three resonance contributors (A) whereas reaction at C3 gives an arenium ion with only two resonance contributors (B). Therefore, pyrrole is expected to give the C2 substituted product as the major product.
Chemicals from Aromatic Hydrocarbons
Published in James G. Speight, Handbook of Petrochemical Processes, 2019
The nitration reaction occurs with an electrophilic substitution by the nitronium ion. The reaction conditions are milder than those for benzene due to the activation of the ring by the methyl substituent and a mixture of NT derivatives is the result. The two important monosubstituted NT derivatives are o- and p-nitrotoluene derivatives.
Twelve Principles of Green Chemistry
Published in Vera M. Kolb, Green Organic Chemistry and Its Interdisciplinary Applications, 2017
This is a classical experiment that illustrates the principles of electrophilic aromatic substitution. The electrophile is NO2+ (nitronium ion). According to the theory, the predominant product should be the m (meta) isomer, which is shown in Figure 2.1, rather than the other two possible isomers, namely, o (ortho) or p (para) isomers. The structures of all three isomers are shown in Figure 2.2.
Complexes of copper(I) with aromatic compounds facilitate selective electrophilic aromatic substitution
Published in Journal of Coordination Chemistry, 2018
Magal Saphier, Inna Levitsky, Alexandra Masarwa, Oshra Saphier
The mechanism of the aromatic nitration substitution reaction was studied intensively over the years; it proceeds as an electrophilic substitution reaction that occurs with the active intermediate nitronium ion, NO2+. Brønsted acid sites are responsible for the generation of NO2+ from nitric acid. Thus, the catalytic activity depends on Brønsted acidity. Brei et al. [6] explained that strong Brønsted sites are necessary for an effective formation of intermediate NO2+ ions from nitric acid. Furthermore, Mishra et al. [7] reported that Brønsted acid sites are responsible for the NO2+ formation while Lewis sites favor the formation of para substituted product.