Reactivity: How and Why - Organic Chemistry Concepts: An EFL Approach - page 65

CHAPTER 5
Reactivity: How and Why

5.1 WHY DO REACTIONS OCCUR?
This chapter will show you how to use the concepts of shape and electronic
structure of organic compounds to find out what types of reaction the com-
pounds undergo. We use the models of hybridization, inductive effect, and delo-
calization to help us understand how and why organic reactions occur.

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5.2 BOND BREAKING AND MAKING
Bonds are broken and made in all chemical reactions. With covalently bonded
atoms, there are two ways for the two-electron bond to break. These are shown
in Figure 5.1 .

The first way, homolysis , is the symmetrical sharing of the bonding electrons
and leads to two radicals. Each radical has one unpaired electron from the origi-
nal bonding pair. The second way, heterolysis , is the unsymmetrical sharing
of the bonding electrons and leads to ions. The negatively charged anion has
both original bonding electrons and the positively charged cation has an empty
orbital.

FIGURE 5.1
Bond-breaking processes.

Figure 5.2 shows that the reverse is true for covalent bond making. If radicals
combine, we call this homogenic bond making. If a cation and an anion com-
bine, we call this heterogenic bond making.

FIGURE 5.2
Bond-making processes.