The Foundations of Chemistry

HYDROCARBONS: A SUMMARY

Hydrocarbons contain only carbon and hydrogen. They can be subdivided into various

groups. To assist you in organizing what you have studied so far in this chapter, take a

few minutes and study Figure 27-13.

FUNCTIONAL GROUPS

The study of organic chemistry is greatly simplified by considering hydrocarbons as parent

compounds and describing other compounds as derived from them. In general, an organic

molecule consists of a skeleton of carbon atoms with special groups of atoms attached to

that skeleton. These special groups of atoms are often called functional groupsbecause

they represent the most common sites of chemical reactivity (function). The only func-

tional groups that are possible in hydrocarbons are double and triple (i.e., pi) bonds. Atoms

other than C and H are called heteroatoms,the most common being O, N, S, P, and

the halogens. Most functional groups contain one or more heteroatoms.

In the next several sections we will introduce some common functional groups that

contain heteroatoms and learn a little about the resulting classes of compounds. We will

continue to represent alkyl groups with the symbol RX. We commonly use that symbol

to represent either an aliphatic (e.g., alkyl) or an aromatic (e.g., an aryl such as phenyl)

group. When we specifically mean an aryl group, we will use the symbol ArX.

ORGANIC HALIDES

Almost any hydrogen atom in a hydrocarbon can be replaced by a halogen atom to give

a stable compound. Table 27-7 shows some organic halides and their names.

27-8

27-7

As you study the following sections,
you may wish to refer to the summary
in Section 27-15.

1064 CHAPTER 27: Organic Chemistry I: Formulas, Names, and Properties

1000 lb of coal tar

distilled yields:

Light oil

redistilled

yields approx.:

16 lb Benzene

2.5 lb Toluene

0.3 lb Xylene

Middle oil

extracted

with NaOH

and redistilled:

Phenol

and

cresols

together

about

20 lb

Naphthalene

40–60 lb

Heavy oil

yields

impure cresols

and phenols

Green oil

yields

anthracene

and

phenanthrene

5–20 lb

Pitch

500–

600 lb

Figure 27-12 Fractions obtained from coal tar.

See the Saunders Interactive
General Chemistry CD-ROM,
Screen 11.5, Functional Groups.