Electrophilic Aromatic Substitution (EAS)

A chemical reaction where an electrophile (electron-loving species) substitutes a hydrogen atom on a benzene ring. This process is fundamental to the synthesis of many aromatic compounds.

A resonance-stabilized carbocation formed during the EAS reaction. It results from the attack of an electrophile on the benzene ring, leading to the formation of a new sigma bond between the electrophile and the ring.

A reaction where bromine (Br2) is added to a benzene ring, leading to the formation of a bromobenzene molecule. This reaction is an important example of an EAS reaction.

A reaction used to introduce a nitro group (NO2) onto a benzene ring. This reaction is crucial for the synthesis of many aromatic compounds containing nitro groups.

Substituents on a benzene ring can influence the rate and position of further EAS reactions. These effects are a combination of resonance and inductive effects.

Groups that increase the electron density of the benzene ring, making it more reactive to electrophilic attack.

Groups that withdraw electron density from the benzene ring, making it less reactive to electrophilic attack.

EDGs increase the rate of electrophilic aromatic substitution (EAS) compared to benzene, making the ring more reactive. EWGs decrease the rate of EAS, making the ring less reactive.

Halogens (-F, -Cl, -Br, -I) are unique substituents that act as deactivating groups in electrophilic aromatic substitution but direct the incoming electrophile to the ortho and para positions.

The relative reactivity of benzene derivatives in electrophilic aromatic substitution reactions is directly related to the nature of the substituents attached to the ring. Electron-donating groups (EDGs) increase reactivity, while electron-withdrawing groups (EWGs) decrease reactivity.

The stability of intermediates in electrophilic aromatic substitution (EAS) reactions determines the preferred position of attack (ortho, meta, or para). Stabilized intermediates are formed more readily, leading to the favored product.

The methyl group (CH3) in toluene acts an electron-donating group (EDG), making toluene significantly more reactive than benzene in electrophilic aromatic substitution reactions.

The formation of ortho and para products in electrophilic aromatic substitution reactions is favored because the intermediates involved in these reactions benefit from additional stabilization through resonance.

The intermediates for meta-attack in electrophilic aromatic substitution are less stable compared to those for ortho and para attack due to the absence of a tertiary carbocation resonance structure, leading to a slower reaction rate.

The rate of electrophilic aromatic substitution for nitrobenzene is significantly slower than for benzene.

Electron-withdrawing groups (EWGs) like nitro groups (-NO2) direct electrophilic attack to the meta position.

Halogens are deactivating groups in EAS but are considered ortho/para directing. This is due to a battle: inductive withdrawal makes the ring less reactive, but resonance donation stabilizes the sigma complex for ortho/para.

A reaction is said to be 'deactivating' if the rate of reaction with that group is slower than that of benzene.

Alkyl groups increase the reactivity of a benzene ring toward electrophilic aromatic substitution (EAS) because they donate electron density through sigma bonds. This effect makes the ring more susceptible to attack by electrophiles.

Alkyl groups on a benzene ring direct incoming electrophiles to the ortho and para positions. This is due to the stabilization of the sigma complex formed in those positions by resonance, including a tertiary carbocation.

A methoxy group (OCH3) attached to a benzene ring strongly activates the ring towards electrophilic attack, leading to a faster reaction rate compared to benzene or toluene. This is because the oxygen atom donates electron density into the ring through resonance, stabilizing the transition state and the sigma complex mainly at the ortho and para positions.

Electron-withdrawing groups (EWGs) on a benzene ring generally decrease the rate of electrophilic aromatic substitution (EAS) compared to benzene.

Electron-withdrawing groups (EWGs) on a benzene ring typically direct incoming electrophiles to the meta position. This is because the sigma complex formed at the meta position is less destabilized by the positive charge on the EWG.

The sigma complex formed in electrophilic aromatic substitution (EAS) is highly destabilized when the positive charge is adjacent to an electron-withdrawing group (EWG). This is because they both possess partial positive charges, causing electrostatic repulsion.

Anisole (methoxybenzene) reacts with bromine much faster than benzene without a catalyst because the methoxy group strongly activates the ring. This rapid reaction leads to tribromination.

Aniline (aminobenzene) reacts with bromine rapidly, leading to tribromination, as the amino group is a strong activator.

A reaction in which an acyl group (R-C=O) replaces a hydrogen atom on a benzene ring, forming a phenyl ketone. It typically uses acyl chlorides and a Lewis acid catalyst. Polyacylation is less likely due to the phenyl ketone's lower reactivity compared to benzene.

A chemical reduction method used to convert aromatic ketones (acyl benzenes) into alkyl benzenes. It employs amalgamated zinc and aqueous hydrochloric acid.

The position on an aromatic ring adjacent to a carbon atom directly attached to the ring, where substitution or reaction is more likely because of the stabilizing effect of the resonance structure.

A reaction that introduces a halogen atom (typically bromine) onto the benzylic position of an aromatic compound. This reaction often makes use of radical chemistry and bromine.

A substituent with an electronegative atom like Br, drawing electron density away from the benzene ring, making it less reactive toward electrophilic attack. It directs incoming electrophiles to the meta position.

A substituent containing a nitro group that pulls electron density away from the benzene ring, making it less reactive towards electrophilic attack. It directs the incoming electrophile to the meta position.

The order of reactions is important for determining which product is formed. Nitration first, then alkylation, will give you the desired p-nitro-t-butylbenzene because nitration will direct the alkyl group to the desired position.

An electrophilic aromatic substitution reaction where a bromine atom substitutes a hydrogen atom on a benzene ring.

A carbocation is formed from the reaction of an alkyl halide with a Lewis acid. This carbocation is the electrophile in the Friedel-Crafts alkylation reaction.

If two directing groups are present on a benzene ring, the stronger activating group will determine the position of the incoming electrophile. For example, a stronger activating group like an amino group will direct the incoming electrophile to the ortho and para positions, even if another group present is meta directing.

Friedel-Crafts alkylation reactions are limited by certain factors such as the presence of deactivating groups on the benzene ring.