Chapter 4. A BRIEF SURVEY OF ORGANIC REACTIONS

Millions of organic compounds undergo millions of chemical transformations and, at first sight, organic chemistry could be considered a mere collection of infinite numbers of disconnected facts. There are only a few general concepts that can be applied to most chemical reactions. In fact modern organic chemistry is a very logical subject, therefore the best way to learn it consists in understanding concepts but not in memorization of numerous facts.

This chapter is concerned with fundamental types of organic reactions, classification of reactants, and general description of the reactions.

4.1. TYPES OF ORGANIC REACTIONS

While studying organic chemical reactions two aspects should be taken into account: what types of reactions exist and how a reaction proceeds. First it is more reasonable to look at the types of reactions. Organic reactions can be grouped into several types according to the overall result. They are:

•  addition reactions;

•  elimination reactions;

•  substitution reactions;

•  rearrangements (or isomerization reactions);

•  oxidation and reduction reactions;

•  acid-base interactions.

The latter reactions will be discussed in detail in Chapter 6. Other types of reactions listed above will be briefly characterized.

Addition reactions are those in which two substances react to form a single compound. In this case no atom is removed from both reactants. It can be generalized as follows:

An example of this reaction is the addition of a halogen to an alkene:

Elimination reactions are, to some extent, the reverse of addition reactions. The parts of a molecule are removed from adjacent atoms of the reactant to give two products:

One product is an unsaturated compound and the other is usually a small inorganic molecule such as hydrogen, water, ammonia, and so on. The reaction is exemplified in dehydration (elimination of a water molecule) from an alcohol under appropriate conditions: