Aromatic compounds, which are planar cyclic rings with (4n+2)π electrons, will not undergo simple addition reactions like those of alkyl substances. However, in the presence of an electrophile, aromatic compounds will undergo electrophilic aromatic substitution. In this type of reaction, two π electrons from the aromatic ring serve for the ring to act as a nucleophile and attack an electrophile. For nitration, this nucleophile is NO2+, which is produced by reacting nitric and sulfuric acids. After the nucleophile adds, the ring has lost aromaticity. Therefore, the deprotonated acid in solution can pull off a hydrogen from the same carbon that the nitro group has added to, allowing the electrons from that bond to go back into the ring to reproduce aromaticty. There are three possible positions on a benzene ring that a nucleophile could add to, referred to as the ortho, para, or meta positions. In this experiment, the nucleophile will primarily add into the meta position. This is because the starting material is methyl benzoate, as opposed to just benzene. The ester group of methyl benzoate is capable of participating in the resonance of the ring. This withdraws electron density from the benzene ring, and is said to be deactivating. Deactivating substituents destabilize the carbocation intermediates formed from substitutions to the ortho or para positions. This decreases the reaction rate for those positions. Therefore, the meta position is the most reactive one. The mechanism for this reaction is
The product is not likely to undergo further titration at the reaction conditions provided. Generally, polynitrated products do not form except under harsh conditions. For example, the third nitration of toluene in the production of TNT only happens in boiling concentrated sulfuric acid. Although the theory states that there will only be one product, methyl m-nitrobenozate, there are three possible products, so characterization is necessary. This...
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