9.1 Homolytic and Heterolytic Cleavage
For the reactions we learned about so far, bond breaking occurs when one part of the bond takes both electrons (the electron pair) of the bond away. For example, for an SN1 reaction, the leaving group Br leaves with the electron pair to form Br– and carbocation intermediate.
This process is called heterolytic bond cleavage, and the σ bond breaks heterolytically. As before, an arrow with double-barbs is used to show heterolytic cleavage, which is the transfer of the electron pair specifically:
There is another type of bond-breaking process, in which each part of the σ bond takes one electron away, as shown below:
A radical is another highly reactive reaction intermediate, because of the lack of an octet. The substitution reaction we will learn about in this chapter involves the radical intermediate.