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12.4 HYDROCARBON DERIVATIVES H Cl
The hydrocarbons account for only about 5 percent of the known Cl C Cl Cl C Cl
organic compounds, but the other 95 percent can be considered
Cl Cl
hydrocarbon derivatives. Hydrocarbon derivatives are formed
Chloroform Carbon tetrachloride
when one or more hydrogen atoms on a hydro carbon have been
(CHCl 3 ) (CCl 4 )
replaced by some element or group of elements other than hydro-
gen. For example, the halogens (F 2 , Cl 2 , Br 2 ) react with an alkane
Cl
in sunlight or when heated, replacing a hydrogen: H H
F C Cl C C
H Cl
H H F
sunlight Dichlorodifluoromethane Vinyl chloride
H C H + Cl Cl H C Cl + H Cl
(a Freon, CCl 2 F 2 ) (C 2 H 3 Cl)
H H FIGURE 12.13 Common examples of organic halides.

In this particular substitution reaction, a hydrogen atom on
methane is replaced by a chlorine atom to form methyl chloride.
tions. The atom or group of atoms in an organic molecule that
Replacement of any number of hydrogen atoms is possible, and
is the site of a chemical reaction is identified as a functional
a few organic halides are illustrated in Figure 12.13.
group. It is the functional group that is responsible for the chemi-
If a hydrocarbon molecule is unsaturated (has a multiple
cal properties of an organic compound. Functional groups usu-
bond), a hydrocarbon derivative can be formed by an addition
ally have (1) multiple bonds or (2) lone pairs of electrons that
reaction:
cause them to be sites of reactions. Table 12.5 lists some of the
H H H H H H common hydrocarbon functional groups. Look over this list,
comparing the structure of the functional group with the group
H C C C H + Br Br H C C C H name. Some of the more interesting examples from a few of
these groups will be considered next. Note that the R and R′
H H Br Br
(pronounced, “R prime”) stand for one or more of the hydro-
The bromine atoms add to the double bond on propene, form- carbon groups from Table 12.4. For example, in the reaction be-
ing dibromopropane. tween methane and chlorine, the product is methyl chloride. In
Alkene molecules can also add to one another in an ad- this case, the R in RCl stands for methyl, but it could represent
dition reaction to form a very long chain consisting of hun- any hydrocarbon group.
dreds of molecules. A long chain of repeating units is called a
polymer (poly- = many; -mer = segment), and the reaction is
called addition polymerization. Ethylene, for example, is heated
under pressure with a catalyst to form polyethylene. Heating TABLE 12.4
breaks the double bond,
Alkane hydrocarbons and corresponding hydrocarbon groups
H H Alkane Molecular Hydrocarbon Molecular
H H Name Formula Group Formula
C C C C
H H Methane CH 4 Methyl –CH 3
H H Ethane C 2 H 6 Ethyl –C 2 H 5
Propane C 3 H 8 Propyl –C 3 H 7
which provides sites for single covalent bonds to join the ethyl-
Butane C 4 H 10 Butyl –C 4 H 9
ene units together,
Pentane C 5 H 12 Amyl –C 5 H 11
H H H H H H H H Hexane C 6 H 14 Hexyl –C 6 H 13
Heptane C 7 H 16 Heptyl –C 7 H 15
C C + C C C C C C
Octane C 8 H 18 Octyl –C 8 H 17
H H H H H H H H Nonane C 9 H 20 Nonyl –C 9 H 19
Decane C 10 H 22 Decyl –C 10 H 21
which continues the addition polymerization until the chain is
hundreds of units long. Synthetic polymers such as polyethyl- H
ene are discussed in the “Synthetic Polymers” section.
Note: —CH 3 means C H where * denotes unattached. The attachment takes
The addition reaction and the addition polymerization re-
action can take place because of the double bond of the alkenes, H
and, in fact, the double bond is the site of most alkene reac- place on a base chain or functional group.

12-9 CHAPTER 12 Organic Chemistry 307