Chemistery

The first step of EAS is highly endothermic as the aromaticity is lost. Therefore, we need a strong electrophile  to initiate the reaction. If we want to do bromination , we cannot use Br2 directly because it is not a strong electrophile  (Br2 has no open octect  and it is nonpolar, no formal charges). We enhance its electrophilicity  by using a Br2.FeBr3 (or Br2.AlBr3 ) intermediate (FeBr3 or AlBr3 is a Lewis acid , electron acceptor, so it withdraws the electrons from Br, making it much more polar). The Fe-Br bond is more polar so that the Br is a stronger  electrophile .  The rest follows the general mechanism pattern. The electrophile  attacks the benzene ring, forming a sigma complex. Then a proton is lost, giving off HBr and achieving aromaticity again. Chlorination is basically the same with the chlorine group instead of the bromine group.  EAS: Bromination The sigma complex is stabilized by resonance: ...

Aromatic compounds are widely used in organic chemistry. To master the chemistry of aromatic compounds, we have to know EAS and NAS, which stands for Nucleophilic Aromatic Substitution and Electrophilic Aromatic Substitution respectively. Aromatic compounds are hydrocarbons contain a benzene (which has an aromatic ring). Let's have an overview of the steps of reaction happening in an EAS. Electrophilic attack the ring (resonance stabilized)  Base abstract proton  Here is the general two-step mechanism: EAS The intermediate is a resonance-stabilized carbocation  called  sigma complex (arenium ion) and it is not aromatic anymore. The first step is highly endothermic because of the loss of aromaticity (aromatic compound is more stable).   Here are the resonance forms: sigma complex After going through the general mechanism, we will then discuss the specific EAS reactions in the following order: Halogenation  (Bromination ...