Reactions of Aromatic Compounds By Dr. Mohammad
Just like an alkene, benzene has clouds of p electrons above and below its sigma bond framework.
Although the p electrons are in a stable aromatic system, they are still available for reaction with strong electrophiles.
This generates a carbocation which is resonance stabilized (but not aromatic).
This cation is called a sigma complex because the electrophile is joined to the benzene ring through a new sigma bond.
The sigma complex (also called an arenium ion) is not aromatic since it contains an sp3 carbon (which disrupts the required loop of p orbitals).
The loss of aromaticity required to form the sigma complex explains the highly endothermic nature of the first step. (That is why we require strong electrophiles for reaction).
The sigma complex wishes to regain its aromaticity, and it may do so by either by a reversal of the first step (i.e. regenerate the starting material) or by loss of the proton on the sp3 carbon (leading to a substitution product).
When a reaction proceeds this way, it is electrophilic aromatic substitution.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .