The separation of mixtures of compounds to give the pure components is of great practical importance in chemistry. Many synthetic reactions give mixtures of products and it is necessary for you to have a reasonably clear idea of how mixtures of compounds can be separated. Almost all compounds of biochemical interest occur naturally as components of very complex mixtures from which they can be separated only with considerable difficulty.

Separations can be achieved by differences in physical properties, such as differences in boiling point, or by chemical means, wherein differences in physical properties are enhanced by chemical reactions. In this chapter we will consider some separations of compounds based on differences in physical properties. Chemical procedures will be discussed elsewhere in connection with the appropriate classes of compounds.

Identification and structure determination are often closely allied to the problem of separation. Once a compound is separated, how do we determine whether it is identical to some previously known compound (identification) or, if that can't be done, how do we determine its chemical structure? The spectroscopic properties of molecules have proven to be extremely informative for both identification and structure determination and this chapter is mainly concerned with the application of spectroscopy for such purposes. We will give you now an overview of the spectroscopic properties of the major classes of organic compounds. In subsequent chapter, spectroscopic properties will be discussed in the context of the class of compounds under consideration.