wk7,8 - advanced aromatic chemistry

What is EAS?

Electrophilic Aromatic Substitution – an electrophile replaces H on a benzene ring.

What are the two steps of EAS?

Addition (electrophile attacks) → Elimination (H⁺ leaves).

What is the intermediate in EAS called?

Wheland intermediate (non-aromatic cation).

What reagents are used for nitration?

HNO₃ + H₂SO₄.

What reagents are used for bromination?

Br₂ + FeBr₃.

What reagents are used for Friedel-Crafts alkylation?

R–Cl + AlCl₃.

What reagents are used for Friedel-Crafts acylation?

R–CO–Cl + AlCl₃.

What is an EDG?

Electron-donating group (e.g., OH, OCH3, NH2, CH3).

What is an EWG?

Electron-withdrawing group (e.g., NO2, CN, CHO, COOH).

Where does an EDG direct in EAS?

ortho and para.

Where does an EWG direct in EAS?

meta.

Do EDGs make EAS faster or slower?

Faster (activate).

Do EWGs make EAS faster or slower?

Slower (deactivate).

Do halogens activate or deactivate in EAS?

Deactivate (slower) but direct ortho/para.

What is SₙAr?

Nucleophilic Aromatic Substitution – a nucleophile replaces a leaving group on a benzene ring.

What two things does a ring need for SₙAr?

A good leaving group (halogen) and an EWG.

What is the intermediate in SₙAr called?

Meisenheimer complex (non-aromatic anion).

Does adding more EWGs make SₙAr faster or slower?

Faster (more stabilisation of the intermediate).

What is benzyne?

A very unstable intermediate with a triple bond in a benzene ring.

What conditions are needed for benzyne?

Strong base + high temperature (~350°C).

Does benzyne require EWGs?

No.

Why does benzyne give two products?

The triple bond is symmetrical; the nucleophile can attack at either end.

What is a diazonium salt?

An aromatic compound with a –N₂⁺ group.

How do you make a diazonium salt?

Aniline + NaNO₂ + HCl at 0–5°C.

Why is the diazonium reaction called Sₙ1?

Because N₂ leaves first (unimolecular step), then the nucleophile attacks.

What is the Sandmeyer reaction?

Using CuCl, CuBr, or CuCN with a diazonium salt to make Ar–Cl, Ar–Br, or Ar–CN.

What reagent gives Ar–I from a diazonium salt?

KI (no copper needed).

What reagent gives Ar–OH from a diazonium salt?

H₂O, warm.

What is the key difference between EAS and SₙAr?

EAS: electrophile attacks, needs EDG. SₙAr: nucleophile attacks, needs EWG.

What is the key difference between SₙAr and benzyne?

SₙAr needs EWGs; benzyne does not but needs harsh conditions.