Aromatic Directing Effects Flashcards

Vocabulary practice flashcards covering aromaticity, electrophilic aromatic substitution mechanisms, electronic directing effects, and Friedel-Crafts reactions based on lecture notes.

Electrophile

An electron-loving species that is electron deficient or positively charged, toward which electrons flow during a reaction.

Nucleophile

A nucleus-loving species that is electron rich or negatively charged, from which electrons flow toward an electron-deficient center.

Benzene

An aromatic hydrocarbon with six equivalent $1.39$\,\text{Å} C-C bonds that is $140\,kJ\,mol^{-1}$ more stable than cyclohexatriene due to resonance stabilization.

Wheland Intermediate

A non-aromatic, delocalized carbocation intermediate formed during electrophilic aromatic substitution, which is stabilized by resonance forms before losing a proton to restore aromaticity.

Electrophilic Aromatic Substitution (Ar-SE)

A reaction mechanism where an electrophile replaces a hydrogen atom on an aromatic ring via addition to form a carbocation intermediate, followed by loss of a proton.

Inductive Effect ($I$)

An electrostatic electronic effect resulting from the electronegativity difference across a bond, falling off with distance, categorised as $-I$ (electron withdrawing) or $+I$ (electron donating).

Resonance Effect ($R$)

An electronic effect (also called mesomeric effect) resulting from the conjugation of lone pair or $π$ electrons with the $π$-system of an aromatic ring.

Hyperconjugation

A mechanism of electron release or withdrawal involving the overlap of C-H or C-C $σ$ bonds with the $π$ system of an unsaturated ring, where C-C hyperconjugation is more significant than C-H hyperconjugation.

Friedel-Crafts Alkylation

An electrophilic aromatic substitution reaction that introduces an alkyl group onto a benzene ring using an alkyl halide, aliphatic alcohol, or alkene precursor with an acid catalyst.

Friedel-Crafts Acylation

An electrophilic aromatic substitution reaction where acid chlorides or acid anhydrides react with an aromatic ring in the presence of a Lewis acid catalyst to yield an aryl ketone.

Acylium Ion

The reactive cation intermediate formed during Friedel-Crafts acylation when a Lewis acid abstracts a halide from an acyl halide.

Ortho Position

The 1,2-position relationship between two substituents on a benzene ring.

Meta Position

The 1,3-position relationship between two substituents on a benzene ring.

Para Position

The 1,4-position relationship between two substituents on a benzene ring.

$p$-Toluenesulfonic Acid (PTSA)

A weighable solid compound (also known as tosic acid or TsOH) produced by the sulfonation of toluene, commonly used as a source of Brønsted acid catalyst.

Activating Substituent

A substituent (such as $-O^-$, $-OH$, $-NH_2$, or alkyl groups) that donates electron density to an aromatic ring, increasing its reactivity toward electrophiles and directing incoming groups to the ortho/para positions.

Deactivating Substituent

A substituent (such as $-NO_2$, $-SO_2OH$, or $-CO_2H$) that withdraws electron density from an aromatic ring, decreasing its reactivity toward electrophiles and directing incoming groups to the meta position.