Chemistry Reference
In-Depth Information
ENRICHMENT
Petroleum is a mixture of many compounds,
mainly hydrocarbons containing varying numbers of
carbon atoms per molecule. Hydrocarbons with more
than 12 carbon atoms per molecule are oily, greasy, or
waxy substances. To produce smaller molecules, which
are characteristic of hydrocarbons used as fuels, oil
companies
crack
the petroleum by heating it in the
absence of air. The heating causes some of the carbon-
carbon bonds to break and results in the production of
a range of smaller molecules. Cracking in the presence
of certain catalysts optimizes the yield of those isomers
that are useful as fuels. The cracking process is fol-
lowed by distillation, in which various types of petro-
leum products are separated from one another by
means of their different boiling points. Two isomers of
octane, are shown in Figure 20.6. The fuel
known as “100 octane” is 2,2,4-trimethylpentane.
C
8
H
18
,
CH
3
W
CH
3
W
Two Isomers of
Figure 20.6
Octane
CH
3
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
3
CH
3
CCH
2
CHCH
3
CH
3
Octane
2,2,4-Trimethylpentane
Isomers exist in all classes of organic compounds, some of which are
described in the next section.
Snapshot Review
❒
Isomers of hydrocarbons are produced by differences in the position
of carbon atoms or of multiple bonds or both.
❒
Numbering of carbon chains starting at both ends is done for single
branches only.
ChemSkill Builder 24.1
A. What is the molecular formula of the smallest member of each
nonaromatic series that exists in isomeric forms?
B. Write the line formula of each of the three unbranched heptynes, and tell
how their names distinguish them.
20.3
Other Classes of Organic Compounds
Awide variety of organic compounds contain at least one other element in addi-
tion to carbon and hydrogen. The other elements most commonly found in
organic compounds are all nonmetals—oxygen, nitrogen, fluorine, chlorine,
bromine, iodine, sulfur, and phosphorus. The
total bond order
of an atom is
its number of bonding electron pairs. Just as a hydrogen atom always shares
one electron pair to form one covalent bond and a carbon atom shares four elec-
tron pairs in organic compounds (in four single bonds, two double bonds, two
single bonds and one double bond, or one single bond and one triple bond),
these other elements also have characteristic total bond orders in neutral mole-
cules (Table 20.3). Knowing these total bond orders is essential to interpreting
line formulas correctly.
