Chapter 10: Radicals

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

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

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