Chemistry of Benzene: Electrophilic Aromatic Substitution

This set of vocabulary flashcards covers the fundamental concepts of Electrophilic Aromatic Substitution, including specific reaction types, substituent effects (inductive and resonance), directing groups, nucleophilic aromatic substitution, benzyne intermediates, and side-chain reactions of benzene derivatives.

Electrophilic Aromatic Substitution (EAS)

A reaction where an electrophile reacts with an aromatic ring to substitute a hydrogen on the ring.

$$FeBr_3$$

A catalyst used in the electrophilic bromination of benzene to generate the reactive electrophile from $Br_2$.

Nitronium ion

The reactive electrophile ($NO_2^+$) produced by the combination of concentrated nitric acid ($HNO_3$) and sulfuric acid ($H_2SO_4$).

Aromatic Sulfonation

A reaction occurring with fuming sulfuric acid (a mixture of $H_2SO_4$ and $SO_3$) where the reactive electrophile is either $HSO_3^+$ or neutral $SO_3$.

TEDA (triethyldiamine)

A reagent used to promote aromatic substitution reactions, specifically mentioned in the context of fluorination (F-TEDA-$BF_4$).

Friedel–Crafts Alkylation

The treatment of an aromatic compound with an alkyl chloride and an $AlCl_3$ catalyst to yield a carbocation electrophile that substitutes onto the ring.

Friedel–Crafts Acylation

The reaction of an aromatic ring with a carboxylic acid chloride in the presence of $AlCl_3$ resulting in an acyl group substitution via a resonance-stabilized acyl cation.

Activation

An effect where a substituent increases the reactivity of the aromatic ring relative to benzene by donating electrons and stabilizing the carbocation intermediate.

Deactivation

An effect where a substituent decreases the reactivity of the aromatic ring relative to benzene by withdrawing electrons and destabilizing the carbocation intermediate.

Meta Directors

Substituents such as carbonyl groups ($C=O$), cyano groups ($CN$), nitro groups ($NO_2$), quaternary ammonium groups ($N(CH_3)_3^+$), and sulfonic acid groups ($SO_3H$) that direct electrophilic substitution to the 3-position.

Inductive effect

The withdrawal or donation of electrons through a $\sigma$ bond due to the electronegativity of a substituent.

Resonance effect

The withdrawal or donation of electrons through a $\pi$ bond due to the overlap of a p orbital on the substituent with a p orbital on the aromatic ring.

Hyperconjugation

The delocalization of $\sigma$ electrons from a $C-C$ or $C-H$ bond into an empty or partially filled p orbital, used by alkyl groups to inductively donate electrons.

Nucleophilic Aromatic Substitution

A reaction where the aromatic ring acts as an electrophile and a leaving group (such as a halide) is replaced by a nucleophile; it requires the presence of strong electron-withdrawing groups in ortho or para positions.

Carbanion intermediate

A resonance-stabilized intermediate with a negative charge formed during nucleophilic aromatic substitution.

Sanger’s reagent

A reagent that reacts with proteins via nucleophilic aromatic substitution to attach a label to one end of the protein chain.

Benzyne

A highly reactive chemical intermediate with the electronic structure of a distorted alkyne, formed by the elimination of $HX$ from halobenzenes without electron-withdrawing substituents.

Side-chain Oxidation

A process where alkyl side chains on an aromatic ring are converted to carboxyl groups ($-CO_2H$) using oxidizing agents like $KMnO_4$ or $O_2$ with $Co(III)$, provided benzylic hydrogens are present.

N-bromosuccinimide (NBS)

A reagent used for the bromination of alkylbenzene side chains specifically at the benzylic position through a radical mechanism.

Benzylic radical

A resonance-stabilized intermediate where an unpaired electron is shared by the ortho and para carbons of the aromatic ring, facilitating side-chain bromination.

Catalytic Hydrogenation (Benzene)

The reduction of an aromatic ring to a cyclohexane using a platinum catalyst at high pressure or catalysts like rhodium on carbon.