This chapter discusses the reactions of compounds that have an electronegative atom or group of atoms attached to an sp3-hybridized carbon.
We start chapter 9 looking at the reactions of alkyl halidescompounds in which the electronegative atom is a halogen. In this chapter, we see that the electronegative halogen atom can be replaced by another atom or group of atoms. This is called a substitution reactionone group substitutes for another. How easy it is to replace the group depends on how tightly it is bonded to the sp3-hybridized carbon. Because weak bases share their electrons less well than strong bases (and, therefore, are less tightly bonded than strong bases), we see that weaker bases can be substituted more readily than stronger bases.
In addition to being able to undergo substitution reactions, alkyl halides can also undergo elimination reactions. In an elimination reaction, the electronegative atom is removed along with a hydrogen from an adjacent carbon. In an elimination reaction, two sigma bonds are broken and are replaced by a pi bond. Be sure to look carefully at Table 9.5. There is a lot of material to keep straight, and this table should make it a little easier for you.