Electrophilic Aromatic Substitution Reactions

Vocabulary flashcards for definitions and key terms related to Electrophilic Aromatic Substitution Reactions.

Electrophilic addition reaction

Reaction where a new atom or group of atoms adds to both carbons involved in the double bond.

σ-complex

Intermediate carbocation formed when the electron cloud of the π bond reacts with the electrophile.

sp3

The carbon that receives the electrophile in an electrophilic aromatic substitution becomes hybridized.

Electrophilic aromatic substitution

Reaction type where an electrophile substitutes itself for a hydrogen on the ring.

First step

Step in the mechanism of an electrophilic substitution reaction that is the rate-determining step.

Electrophilic reagent

Reagent used in an electrophilic aromatic substitution to synthesize substituted aromatic compounds.

Nitrobenzene

Product of the reaction between benzene and hot concentrated nitric acid.

Nitronium ion (NO2+)

Electrophile in the nitration of benzene to form nitrobenzene.

Concentrated sulfuric acid

Substance added to a reaction mixture to increase the concentration of the nitronium ion.

Deuterium (2H abbreviated as D)

Isotope of hydrogen with twice the mass of hydrogen.

Lewis acid

Conversion of benzene to bromobenzene or chlorobenzene by electrophilic aromatic substitution requires the presence of a _.

Iron(III) chloride or iron(III) bromide

Catalyst in the conversion of benzene to bromobenzene or chlorobenzene.

Fluorination of benzene

Reaction that requires special conditions and reaction vessels because it is very exothermic.

Iodination of benzene

Reaction that requires special techniques to iodinate directly, such as adding iodine in the presence of a strong oxidizing reagent.

Sulfonation reaction

Reaction where benzene reacts with sulfuric acid to produce benzenesulfonic acid.

Sulfur trioxide

The actual electrophile, or sulfonating agent, in a sulfonation reaction.

Friedel-Crafts reaction

Reaction developed by Charles Friedel and James M. Crafts to produce alkylbenzenes and acylbenzenes.

Aluminum chloride

Lewis acid frequently used in a Friedel-Crafts alkylation.

Rearrangement of the alkyl group

Limitation of the Friedel-Crafts reaction where the alkyl group can rearrange.

FeCl3, ZnCl2, and BF3

Lewis acids other than AlCl3 that catalyze Friedel-Crafts reactions.

Alcohol reaction with Lewis acids

Reaction where alcohols in acidic media undergo reactions comparable to the reactions of alkyl halides with Lewis acids.

Friedel-Crafts acylation reaction

A variation of the Friedel-Crafts reaction involving the reaction of an acyl halide or an acid anhydride and a Lewis acid with benzene to yield an acylbenzene.

Halide ion

Leaving group in an acyl halide during Friedel-Crafts acylation.

Carboxylate ion

Leaving group in an acid anhydride during Friedel-Crafts acylation.

One mole of AlCl3 per mole of acyl halide

Amount of AlCl3 needed to react in acylation reactions.

Acylium ion is resonance stabilized

Reason why cations in Friedel-Crafts acylation reactions do not rearrange.

Acylation-reduction sequence

Synthetic strategy where chemists first do an acylation reaction to form a ketone, then they reduce the carbonyl of the ketone to a -CH2- group.

Clemmensen reduction

Reaction that involves heating the ketone with a zinc-mercury amalgam in concentrated HCI.

Wolff-Kishner reduction

Reduction that involves heating the ketone with hydrazine (NH2NH2) and potassium hydroxide in a high boiling alcohol solvent.

Regiochemistry and rate of the reaction

What the substituent on the benzene ring affects in an electrophilic substitution.

Ortho, para directing group

Term for a methyl substituent because toluene produces predominantly ortho and para substitution products.

Meta director

Term for a trifluoromethyl group because substitution in (trifluoromethyl)benzene occurs primarily at the meta position.

Direct them primarily to the ortho and para positions

Effect of electron donating substituents on incoming electrophiles.

Direct them to the meta position

Effect of electron-withdrawing substituents on incoming electrophiles.

Positive charge of the σ complex

The directing effect of the existing substituent group on the arene is based on the interaction of that group with the __.

Activate the aromatic ring with respect to benzene

General trend for ortho, para directors effect on the aromatic ring.

Deactivate the ring

General trend for meta directors effect on the aromatic ring.

Five

Number of rules that summarize Table 2.2

Halogens

Exception to the general rules of how substituents on benzene behave.

All the substituents exert their combined effects

What happens when a benzene ring has two or more substituents.

All available sites are equivalent

Term for when all available sites on a benzene ring with multiple substituents are equivalent.

Substituent with the greatest influence controls the outcome

What happens when substituents have directing influences that oppose one another.

Polycyclic aromatic hydrocarbon

Term for naphthalene, a ten carbon bicyclic aromatic hydrocarbon.

C1 and C2

Positions available for attack by the electrophile in the nitration reaction of naphthalene.

Aryl diazonium salts

Salts that chemists synthesize from aryl amines.

Azo coupling

Reaction of diazonium salts used as electrophiles to substitute onto another aromatic system.

Azo functional group (-N=N-)

Functional group found in the products formed in azo coupling reactions.

Azo dyes

Term for azo compounds that are highly colored and make excellent dyes.

Sandmeyer reaction

Reaction where the diazonium salt reacts with copper(l) chloride, bromide, or cyanide to replace the - N2 + group on the ring.

Schiemann reaction

Reaction where fluoroboric acid (HBF4) is added to the diazotization reaction medium and heated to form the aryl fluoride.

Directive influences of each group

Influence that determines the reaction sequence when planning a synthesis to prepare a benzene compound with several substituents from benzene.