NH 2, -NR 2 > -OH, -OR> -NHCOR> -CH 3 and other alkyl groups Examples of activating groups in the relative order from the most activating group to the least activating:.As a consequence, the introduction of a second substituent in the aromatic can occur in position ortho, meta, or para depending on the electron effects induced by the previously existing substituent.Ĭlassification of Substituents according to their influence in the reactivity of aromatic rings Deactivated rings: the substituents on the ring are groups that withdraw electrons.These substituents undergo electrophilic aromatic substitution slower than benzeneĪt the same time, not every carbon atom in the aromatic ring is activated or deactivated at the same level.These effects can increase or decrease the electron density on the aromatic, activating or deactivating it. Substituted rings are divided into two groups based on the type of the substituent that the ring carries: Inductive effect is the withdraw of the sigma ( the single bond ) electrons away from the ring toward the substituent, due to the higher electronegativity of the substituent compared to the carbon of the ring. Resonance effect or mesomeric effect is the conjugation between the ring and the substituent, which means the delocalizing of the \(\pi\) electrons between the ring and the substituent. Substituents determine the reaction direction by resonance or inductive effect The deactivating group directs the reaction to the meta position, which means the electrophile substitute the hydrogen that is on carbon 3 with the exception of the halogens that is a deactivating group but directs the ortho or para substitution. The activating group directs the reaction to the ortho or para position, which means the electrophile substitute the hydrogen that is on carbon 2 or carbon 4. These substituents undergo electrophilic aromatic substitution slower than benzene. ![]() Deactivated rings: the substituents on the ring are groups that withdraw electrons.These substituents undergo electrophilic aromatic substitution faster than benzene. Activated rings: the substituents on the ring are groups that donate electrons.Substituted aromatic rings are divided into two groups based on the type of the substituent that the ring carries (A): How can we determine the most likely position? To answer this question, we need to consider the electron effects of the already existing substituent (A) in the electron density of the aromatic ring. However, in this case, the second substituent B could enter the aromatic ring in position ortho, meta, or para. ![]() Once the aromatic ring has undergone an electrophilic aromatic substitution (EAS1), the monosubstitutued benzene can also undergo a second electrophilic aromatic substitution (EAS 2)
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