PART 3. POLY- AND HETEROFUNCTIONAL COMPOUNDS IN LIVING SYSTEMS. Chapter 10. STEREOISOMERISM

As it has already been discussed in Chapter 1, constitutional (or structural) isomers are compounds that have the same molecular formula but different structural formula. There is another type of isomerism, namely stereoisomerism, which is important not only in organic chemistry but, especially, in bioorganic and biological chemistry. The branch of chemistry that concerns with the spatial aspects of molecules is called stereochemistry.

Stereoisomers are compounds that have the same order of atoms attachment, but differ only in the arrangement of their atoms or groups in space.

In other words, stereoisomers are spatial isomers. They can be subdivided into two categories according to the principles by which they are interconverted:

•  configurational isomers that can be interconverted only by breaking a covalent bond and creating a new covalent bond;

•  conformationa! isomers that can be interconverted by rotation about single bonds.

The principal types of isomerism occurring in organic chemistry are summarized below:

Conformational isomerism has been discussed in Chapter 6; in this chapter configurational isomerism will be considered.

Molecules differing only in configuration are termed configurational isomers.

The configuration of a molecule of definite structure is the arrangement of its atoms or groups in space without regard to arrangements that differ only due to rotation about one or more single bonds.