Isomers and Stereochemistry - Organic Chemistry Concepts: An EFL Approach - page 43

CHAPTER 3
Isomers and
Stereochemistry

3.1 WHAT ARE ISOMERS?
Chapters 1 and 2 show that there are many ways to bond together the atoms of
a molecular formula. Isomers are molecules with the same molecular formula,
but with the atoms arranged differently. It is important to understand the rela-
tionships between structures that are isomers. There are different types of rela-
tionships, depending on the way the structures are put together.

43

If we know the causes of various types of isomers, we can understand the
differences in physical and chemical properties between these organic com-
pounds. The same simple ideas extend to the more complex systems found in
nature.

3.2 STRUCTURAL ISOMERS
Structural isomers occur when the atoms of the same molecular formula are
joined in different orders. This gives structurally different molecules that may
have similar physical and chemical properties, Figure 3.1(a) , or not, Figure 3.1(b) .

To interconvert these isomers, relatively high energy is needed to break and
make a number of strong single σ bonds, C-C ∼348 and C-H ∼415 kJ/mol. This
is not usually practical.

(a)

(b)

FIGURE 3.1
Structural isomers.