EASreaktioissa

EASreaktioissa, often translated as "EAS Reactions" in English, refers to electrophilic aromatic substitution reactions. These are a fundamental class of organic chemical reactions where an electrophile replaces a hydrogen atom on an aromatic ring. The aromatic system, characterized by its delocalized pi electrons, is electron-rich and therefore susceptible to attack by electron-deficient species, known as electrophiles.

Common examples of EAS reactions include halogenation, nitration, sulfonation, and Friedel-Crafts alkylation and acylation. In halogenation, a halogen molecule like bromine or chlorine, typically in the presence of a Lewis acid catalyst such as iron(III) bromide or aluminum chloride, acts as the electrophile. Nitration involves the introduction of a nitro group (-NO2) using a mixture of concentrated nitric acid and sulfuric acid. Sulfonation introduces a sulfonic acid group (-SO3H) using fuming sulfuric acid. Friedel-Crafts reactions involve the attachment of alkyl or acyl groups to the aromatic ring, facilitated by Lewis acid catalysts like aluminum chloride.

The mechanism of EAS typically proceeds in two main steps. First, the electrophile attacks the aromatic ring, forming a resonance-stabilized carbocation intermediate called a sigma complex or arenium ion. This intermediate disrupts the aromaticity of the ring temporarily. Second, a base, often the conjugate base of the acid used in the reaction or another nucleophile present, abstracts a proton from the carbon atom that bears the electrophile. This restores the aromaticity of the ring, yielding the substituted aromatic product. The stability of the aromatic system is the driving force for these reactions.