Chapter 10: Radicals

Question 1

Radical Stability Trends

Answer 1

Question 2

Radical Mechanisms

Answer 2

Initiation- the creation of radicals

Propagation- the location of the unpaired electron is moved

Termination- the annihilation of two radicals when they form a bond

Question 3

Radical Halogenation

Alkanes

Answer 3

Reagents

X₂ & hv
ONLY Br₂ & Cl₂
Br₂ has the most synthetic value

Mechanism

Radical hydrogen abstraction first creates the most stable radical intermediate which then abstracts the halogen

Regioselectivity

Chlorine produces a mixture of products with the chlorine NOT always installed at the most stable radical carbon

Bromine is much more regioselective than chlorine; installs at the most stable radical carbon

Stereospecificity

A radical intermediate is effectively trigonal planar with the halogen abstraction equally as likely to occur on either face; produces a mixture of enantiomes

When an additional chiral center is already present an unequal mixture of diastereomers is produced

Question 4

Allylic Bromination

Answer 4

Reagents

NBS & hv

Mechanism

Radical bromination occurs at an allylic position if it is the most stable carbon radical position

If the allylic radical intermediate formed is resonance stabilized halogen abstraction can occur at either site