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Discussion: Electrophilic Aromatic Substitution 1. Nitration of bromobenzene is a type of electrophilic aromatic substitution in which nitric and sulfuric acids introduce a nitro group to a benzene ring. The first step of the reaction if the aromatic ring is not substituted is the aromatic nitration. Benzene +HNO3 –(H2SO4) Benzene-NO2 +H2O. the reaction yields a nitrobenzene. Within the reaction, the nitronium ion that is the result of the HNO3 equilibrium is attacked by the nucleophile or the aromatic ring. This is a classic acid base reaction, the acid being the aromatic ring and the base being the nitronium ion. The result of that reaction is an alpha complex which will react with a base to regenerate the nitro benzene. If the aromatic ring had been substituted like bromobenzene, then it’s a different story. The nitration of bromobenze leads to three different products; 3-bromo- nitrobenzene, 4-bromo-nitrobenzene, and 2-bromo-nitrobenzene. The reason that there are three products instead of one is because of the activiation energies for the attack positions of ortho, para and meta. The activation energy for the meta position is higher those of para, and ortho. The alph- complex of both ortho and para are more stable than the alpha complex of
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This note was uploaded on 12/04/2009 for the course CHE 210 taught by Professor Swinnea during the Spring '08 term at University of Texas at Austin.

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