Chemistry Reference
In-Depth Information
which make up the “backbones” of these organic compounds. Organic com-
pounds in which all of the carbon atoms are bound together by single bonds
are called saturated compounds. If a compound contains two or more car-
bon atoms that are held together by double or triple bonds, the compound
is said to be an unsaturated compound. Figure 4-4a shows propane (C
3
H
8
),
which is a saturated compound, and propyne (C
3
H
4
), which is an unsatur-
ated compound. Why do these two compounds share the same prefix
(“prop-”) and have different suffixes (“-ane” and “-yne”)? This has to do
with the system for naming hydrocarbons, molecules containing only hydro-
gen and carbon.
If a hydrocarbon is saturated—that is, it contains only single bonds—
then it is given the suffix “-ane.” If the hydrocarbon contains one or more
double bonds, then it is given the suffix “-ene.” A hydrocarbon is given the
suffix “-yne” if it contains one or more triple bonds. The prefix associated
with a hydrocarbon is determined by the number of carbon atoms that its
molecule contains. For example, the prefix “meth-” is given to the hydro-
carbon containing only one carbon atom. Methane is a saturated hydro-
carbon (all single bonds) with only one carbon atom. “Prop-” is the prefix
given to hydrocarbons containing three carbon atoms, so both the com-
pounds C
3
H
4
and C
3
H
8
, with three carbon atoms, are given this prefix. The
chart on page 130 shows the prefixes for the first 10 hydrocarbon configu-
rations, along with an example of each.
It may be worth the effort to study the names and formulas of the ex-
amples shown in Figure 4-4b. Do you notice any patterns between the suf-
fixes of the compounds and the relative number of carbon and hydrogen
atoms that they show? Notice all of the compounds with the ending “-ane.”
Can you think of a formula that you can use to determine the number of
hydrogen atoms found in each of the saturated hydrocarbons?
The saturated hydrocarbons are given the group name alkanes, and
they have only single bonds between their carbon atoms. They are all given
the suffix “-ane.” The prefix tells you the number of carbon atoms that an
alkane contains, and you can determine the number of hydrogen atoms
that they contain by using the formula C
n
H
2n+2
where “n” is the number of
carbon atoms in the compound. For example, methane contains one car-
bon atom, so n = 1. The number of hydrogen atoms is determined with
the formula 2n+2, so there are four hydrogen atoms in a molecule of meth-
ane ((2 × 1) + 2 = 4). Propane contains three carbon atoms, so n = 3, and
the number of hydrogen atoms in a molecule of propane would be eight
((2 × 3) + 2 = 8).
