Chemistry Reference
In-Depth Information
Solution
CH
3
W
CH
3
CH
2
CH
2
CH
3
CH
3
CH
2
CH
2
These formulas look less like the same molecule than do the models in Figure
20.5. Be aware, however, that they are representations of the same molecule.
Practice Problem 20.6
Write another condensed formula for butane
that shows both ends of the molecule rotated from the zigzag shape in Figure
20.3c.
As stated previously, compounds with branches on the longest continuous
chain of carbon atoms are named as derivatives of that chain. Each branch is
named using the stem of the alkane having the same number of carbon atoms
with the ending changed to
-yl.
Thus, for the branched chain compound whose
structural formula was illustrated at the beginning of this section, the side chain
is called methyl, and the three-carbon continuous chain is called
propane. Two, three, or four identical side chains are named using the prefix
di-,
tri-,
or
tetra-,
respectively.
CH
3
¬
EXAMPLE 20.7
Does the formula of methylpropane shown previously represent another orien-
tation of the molecule in Example 20.6, or is it another molecule?
Solution
It is another molecule. No amount of rotation about bonds can move the last
carbon atom of the four-carbon chain of butane from the third to the second
carbon atom in the molecule.
Practice Problem 20.7
A student incorrectly named two compounds
(a) 3-methylbutane and (b) 1-methylhexane. Write formulas corresponding to
these names, and give the correct names for the compounds.
EXAMPLE 20.8
Write line formulas for (a) heptane and (b) dimethylbenzene.
Solution
(a)
CH
3
CH
2
CH
2
CH
2
CH
2
CH
2
CH
3
(b)
C
6
H
4
(CH
3
)
2
Practice Problem 20.8
Write a line formula for 2,3,3-trimethylheptane.
