The Foundations of Chemistry

In the IUPAC naming system, the organic halides are named as halo- derivatives of the
parent hydrocarbons. The prefix halo- can be fluoro-, chloro-, bromo-,or iodo-. Simple alkyl
chlorides are sometimes given common names as alkyl derivatives of the hydrogen halides.
For instance, the IUPAC name for CH 3 CH 2 XCl is chloroethane; it is commonly called
ethyl chloride by analogy to HXCl, hydrogen chloride.
A carbon atom can be bonded to as many as four halogen atoms, so an enormous
number of organic halides can exist. Completely fluorinated compounds are known as
fluorocarbonsor sometimes perfluorocarbons.The fluorocarbons are even less reactive
than hydrocarbons. Saturated compounds in which all H atoms have been replaced by
some combination of Cl and F atoms are called chlorofluorocarbonsor sometimes freons.
These compounds were widely used as refrigerants and as propellants in aerosol cans.
However, the release of chlorofluorocarbons into the atmosphere has been shown to be
quite damaging to the earth’s ozone layer. Since January 1978, the use of chlorofluoro-
carbons in aerosol cans in the United States has been banned, and efforts to develop both
controls for existing chlorofluorocarbons and suitable replacements continue. The produc-
tion and sale of freons have been banned in many countries.

Freon is a DuPont trademark for

certain chlorofluorocarbons; other

companies’ related products are

known by other names. Typical freons

are trichlorofluoromethane,

CFCl 3 (called Freon-11), and

dichlorodifluoromethane, CF 2 Cl 2

(called Freon-12).

27- 8Organic Halides 1065

Hydrocarbons

(contain C, H only)

(Sections 27-1 to 27-6)

Aliphatic hydrocarbons

Contain C–C single,

double, and triple bonds,

but no aromatic rings

(Sections 27-1 to 27-4)

Saturated hydrocarbons

Contain only C–C

and

C–H single bonds

(Sections 27–1 and 27–2)

Alkanes, CnH 2 n+2

Contain no rings

methane, ethane,

hexane,

2-methylhexane,

2,2-dimethylpentane

cyclopropane,

cyclopentane,

cyclohexane

Acyclic alkenes, CnH 2 n

ethylene, 1-butene,

2-methyl-1-butene

Cycloalkenes, CnH 2 n–2

cyclopentene,

cyclohexene

Cycloalkanes, CnH 2 n

Contain rings

Alkenes

Contain one or more

C=C double bonds

(Section 27-3)

Polyenes

Contain more than one

C=C per molecule—

e.g., 1,3-butadiene

acetylene, 1-butyne,

3-methyl-1-butyne

benzene, naphthalene,

anthracene, toluene,

p-xylene

Alkynes, CnH 2 n–2

Contain one or more

CC triple bonds

(Section 27-4)

Unsaturated hydrocarbons

Contain one or more

C=C double or

CC triple bonds

(Sections 27-3 and 27-4)

Aromatic hydrocarbons

(Sections 27-5 to 27-6)

SOME EXAMPLES

Figure 27-13 A classification of

hydrocarbons.