Functional groups centers of reactivity

Many organic molecules consist predominantly of a backbone of carbons linked by single bonds, with only hydrogen atoms attached. However, they may also contain doubly or triply bonded carbons, as well as other elements. These atoms or groups of atoms tend to be sites of comparatively high chemical reactivity and are referred to as functional groups or functionalities. Such groups have characteristic properties, and they control the reactivity of the molecule as a whole. 

Hydrocarbons are molecules that contain only hydrogen and carbon 

We begin our study with hydrocarbons, which have the general empirical formula QHj,. Those containing only single bonds, such as methane, ethane, and propane, are called alkanes. Molecules such as cyclohexane, whose carbons form a ring, are called cycloalkanes. Alkanes lack functional groups as a result, they are relatively nonpolar and unreactive. The properties and chemistry of the alkanes are described in this chapter and in Chapters 3 and 4. 

Double and triple bonds are the functional groups of alkenes and alkynes, respectively. Their properties and chemistry are the topics of Chapters 11 through 13. 

A special hydrocarbon is benzene, CeHg, in which three double bonds are incorporated into a six-membered ring. Benzene and its derivatives are traditionally called aromatic, because some substituted benzenes do have a strong fragrance. Aromatic compounds, also called arenes, are discussed in Chapters 15, 16, 22, and 25. 

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