04 Aromatic Compounds in Synthesis Free Online FlashCards

What happens during electrophilic aromatic substitution?

An electrophile replaces a ring hydrogen. The ring forms a resonance-stabilized arenium ion, then loses H⁺ to restore aromaticity.

How do –OH, –OR, and –R direct electrophilic substitution?

Groups such as –OH, –OR, and –R generally activate the ring and direct incoming electrophiles to the ortho and para positions.

How do –NO₂, –CHO, and –CO₂H direct electrophilic substitution?

Groups such as –NO₂, –CHO, and –CO₂H generally deactivate the ring and direct incoming electrophiles to the meta position.

How do halogens affect EAS rate and position?

Halogens deactivate the aromatic ring but direct incoming electrophiles to the ortho and para positions.

How can acylation followed by reduction avoid alkylation rearrangements?

Friedel–Crafts acylation installs –COR without a carbocation rearrangement. Reducing the carbonyl then converts it to –CH₂–.

What is the key intermediate in addition–elimination S_NAr?

In the addition–elimination pathway, a nucleophile adds to the electron-poor ring to form a resonance-stabilized Meisenheimer intermediate; the leaving group then departs.

Where must –NO₂ lie to activate a ring for S_NAr?

An electron-withdrawing group, especially –NO₂, helps when ortho or para to the leaving group by stabilizing the intermediate through resonance. A meta group cannot do so.

What synthetic role do arenediazonium salts serve?

Diazotize an aryl amine to form an arenediazonium salt, then replace the diazonium group with groups such as Cl, Br, I, CN, or OH.

What does nitro-to-amine reduction do?

Reduction with iron or tin under acidic conditions converts an aromatic nitro group, –NO₂, into an amine, –NH₂.

What product does a Birch reduction form from an arene?

Alkali metal in liquid ammonia with an alcohol proton source partially reduces an arene to a 1,4-cyclohexadiene.

What conditions can fully hydrogenate an aromatic ring?

Suitable catalysts and elevated hydrogen pressure can convert an arene to a cyclohexane. More forcing conditions are needed than for hydrogenating an ordinary alkene.

What bond does Suzuki–Miyaura coupling form?

It joins an aryl halide with an arylboronic acid or boronate, typically using palladium and base, to form a biaryl carbon–carbon bond.