License: CC BY-NC-SA: Attribution-NonCommercial-ShareAlike Located at: (Soderberg)/15%3A_Electrophilic_reactions/15.06%3A_Synthetic_parallel_-_electrophilic_aromatic_substitution_in_the_lab. 15.6: Synthetic parallel - electrophilic aromatic substitution in the lab.Located at: (Petrucci_et_al.)/27%3A_Reactions_of_Organic_Compounds/27.06%3A_Electrophilic_Aromatic_Substitution. 27.6: Electrophilic Aromatic Substitution.Vollhardt, Peter. Organic Chemistry : Structure and Function.“On the Mechanism of Sulfonation of the Aromatic Nucleus and Sulfone Formation.” The Journal of Organic Chemistry 66 (1955): 455-465. “Electrophilic Nitration of Aromatics in Ionic Liquid Solvents.” The Journal of Organic Chemistry 66 (Dec. Organic Chemistry, Structure and Function. 4th ed. Belmont, CA: Thomson Learning Inc./ Brooks/Cole, 2005. Brown, William H., Foote, Christopher S., Iverson, Brent L.“Interaction of two functional groups through the benzene ring: Theory and Experiment.” Journal of Computational Chemistry (2008) (p. If we want to understand these data, we need to think about things like π-donation, π-acceptance, inductive effects and cation stability. These regiochemical effects are very closely related to the activating and directing effects we have already seen. Here may be small amounts of ortho– and para– products, but these groups are best described as “ meta-directors”. The other group reacts to make mostly meta-substituted products. Some groups are “ ortho/ para directors”. There may be different ratios of ortho– to para– and there may be small amounts of meta-, but don’t get bogged down in the details. One group reacts to make mixtures of ortho– and para– products. In looking at the table, you might see that there are two groups of substituents. ![]() They reported the following observations: Table : Substitution patterns during nitration of benzene derivatives R in C 6H 5R Ingold and colleagues investigated the question of regiochemistry in nitration. This is often called a +R (for resonance) effect, and this activates the ring towards EAS. Some groups (e.g., H 2N-, HO-, RO-) have lone pairs and act as π-donors, providing additional electron density to the benzene ring via resonance. The roles of these groups are related to their electronic interactions with the electrons in the ring. These groups are called activating groups in this reaction. Substituents that readily donate electron density to the ring, or that effectively stabilize the cationic intermediate, promote the reaction. These groups are called deactivating groups in this reaction. Substituents that draw electron density away from the aromatic ring slow the reaction down. These observations are consistent with the role of the aromatic as a nucleophile in this reaction. Table : Rate of nitration in benzene derivatives R in C 6H 5R Nitrobenzene, C 6H 5NO 2, undergoes the reaction millions of times more slowly. Phenol, C 6H 5OH, undergoes nitration a thousand times faster than benzene does. ![]() In table 1, you can see that some substituents confer a rate of reaction that is much higher than that of benzene (R = H). In the mid-twentieth century, physical organic chemists including Christopher Ingold conducted a number of kinetic studies on electrophilic aromatic substitution reactions. Substituents that make the benzene moor electron-poor can retard the reaction. Because benzene acts as a nucleophile in electrophilic aromatic substitution, substituents that make the benzene more electron-rich can accelerate the reaction.
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