Chemistry Reference
In-Depth Information
EXAMPLE 20.1
Write equations for the reaction of (a) propane with oxygen in limited supply
and (b) ethane with bromine in limited supply.
Solution
(a)
(b)
2 C
3
H
8
(g)
7 O
2
(g) £ 6 CO(g)
8 H
2
O(g)
C
2
H
6
(g)
Br
2
(
/
) £ C
2
H
5
Br(
/
)
HBr(g)
Practice Problem 20.1
Write equations for the reaction of methane
with (a) excess bromine and (b) excess oxygen.
The most modern rules for the systematic naming of alkanes follow:
1. The name is based on the longest continuous chain of carbon atoms in the
molecule.
2. Branches consisting of a hydrocarbon molecule with one hydrogen atom
removed are named with the -
ane
ending replaced by -
yl
. Thus a one-carbon
branch, is called methyl.
3. A branch, functional group (Section 20.3), or multiple bond involving a car-
bon atom in such a chain (see next subsection) is given an “address,” or
position on the carbon chain, which is the number of that carbon atom
counting from the
nearer end
of the chain.
CH
3
¬
,
For example, consider the following condensed formulas:
1
2
3
4
5
5
4
3
2
1
1
2
3
4
5
CH
3
±CH±CH
2
±CH
2
±CH
3
CH
3
±CH
2
±CH
2
±CH±CH
3
CH
3
±CH±CH±CH
2
±CH
3
CH
3
CH
3
Cl
Cl
Compound A
Compound B
Compound C
In compound A, the longest continuous chain is five carbon atoms long, and
there are no multiple bonds, so this compound is named as a
pentane
(see
Table 20.1). The carbon atom to which the methyl group is
attached is identified with the number 2 because that carbon is the second
from the nearer end of the chain. The name is 2-methylpentane. Note that
the number 2 is an
address
and does
not
mean two methyl groups.
The formula for compound B represents the same compound as compound
A but written in the reverse direction. We start numbering the carbon
chain from the end nearer the methyl group, and we get the same name,
2-methylpentane.
We name organic compounds containing chlorine in an analogous manner; com-
pound C is 2,3-dichloropentane.
(CH
3
¬
)
For a compound with only one branch, the carbon chain might be num-
bered as follows:
1
2
3
2
1
C±C±C±C±C
(single branches only)
