Chapter 19 — Free Radical Reactions

What arrow type is used in radical mechanisms?

Single-headed fishhook arrows.

What do fishhook arrows represent?

What do fishhook arrows represent?

How are radicals commonly formed?

How are radicals commonly formed?

Radical stability trend?

Methyl < 1° < 2° < 3° < allylic/benzylic

Why are allylic and benzylic radicals especially stable?

Resonance stabilization.

What are the 3 steps of radical halogenation?

Initiation

Propagation

Termination

What happens in initiation?

Halogen bond breaks homolytically:

Cl₂ → 2 Cl•

What happens in propagation?

Radical abstracts H

Carbon radical reacts with X₂

What happens in termination?

Two radicals combine.

Chlorination vs bromination?

Chlorination = faster, less selective

Bromination = slower, more selective

Which reaction forms more product mixtures?

Chlorination.

Why is bromination more selective?

H-abstraction is endothermic, so radical stability matters more.

What are the main reactions radicals undergo?

H atom abstraction

Addition to double/triple bonds

Combination with other radicals

Oxidation products of alcohols?

1° alcohol → aldehyde → carboxylic acid

2° alcohol → ketone

3° alcohol → no oxidation to carbonyl

What does PCC do?

Oxidizes 1° alcohols only to aldehydes.

What do strong chromium oxidizers do to 1° alcohols?

Oxidize completely to carboxylic acids.