Chapter 6. HYDROCARBONS

We proceed to a study of the chemistry of different classes of organic compounds beginning in this chapter from the simplest ones, hydrocarbons. As it follows from the name, hydrocarbons contain carbon and hydrogen only. They comprise a big series of natural and synthetic compounds. Many hydrocarbons are constituents of petroleum and natural gas. Methane (common name - marsh gas) is the end product of the anaerobic decomposition of organic matter.

6.1. CLASSIFICATION

There are three main types of hydrocarbons, depending on the nature of carboncarbon bonds in a molecule:

•  Saturated hydrocarbons that contain single C-C bonds only;

•  Unsaturated hydrocarbons containing multiple carbon-carbon bonds: a double bond (or bonds), a triple bond (or bonds), or their combination. Single C-C bonds may be also present, of course;

•  Aromatic hydrocarbons that are related in structure to benzene (Sec. 3.2). The first two types are sometimes referred to as aliphatic compounds (from the Greek aleiphas - fat), i. e. compounds of a nonaromatic series.

Hydrocarbons vary considerably in their chemical properties that depend on the nature of the carbon-carbon bonds. This is true also for compounds with various functional groups because hydrocarbons represent a framework of organic molecules.

6.2. SATURATED HYDROCARBONS

These hydrocarbons can be subdivided into two groups, namely, alkanes, compounds with an open carbon chain (linear or branched), and cycloalkanes, compounds with a cyclic carbon skeleton. The rightmost structure in the examples below (decaline) represents a fused-ring system of two cyclohexane rings jointed together.

6.2.1. Conformational Isomerism

Conformations of a molecule of definite configuration are various spatial arrange ments of its atoms that differ only after rotation about C-C single bonds.