The Foundations of Chemistry

Organic molecules are based on a framework of carbon–carbon and carbon–hydrogen

bonds. Many compounds contain onlythe two elements C and H; they are called hydro-

carbons.Hydrocarbons that contain a delocalized ring of pi bonds such as the benzene

ring (Section 9-6) are called aromatic hydrocarbons.Those that do not contain such

delocalized systems are called aliphatic hydrocarbons. Aliphatic hydrocarbons that

contain only sigma (
) bonds (i.e., only single bonds) are called saturated hydrocarbons.

Those that contain both sigma and pi () bonds (i.e., double, triple, or delocalized bonds)

are called unsaturated hydrocarbons.These classifications are diagrammed in Figure

27-1. The first seven sections of this chapter are devoted to the study of hydrocarbons.

A functional groupis a special arrangement of atoms within an organic molecule that

is responsible for some characteristic chemical behavior of the compound. Different mole-

cules that contain the same functional groups have similar chemical behavior. We shall

follow the study of hydrocarbons with a presentation of some important characteristic

functional groups.

1042 CHAPTER 27: Organic Chemistry I: Formulas, Names, and Properties

TABLE 27-1 Hybridization of Carbon in Covalent Bond Formation

Hybridization and Orbitals Used by Bonds Formed by

Resulting Geometry Each C Atom Each C Atom Example

sp^3 , tetrahedral four sp^3 hybrids four 
bonds ethane

sp^2 , trigonal planar three sp^2 hybrids, three 
bonds, ethylene

HH

H H

CC

H

HH

HH

C C H

one porbital one bond

sp, linear two sphybrids, two 
bonds, acetylene

two porbitals two bonds HCCH

See the Saunders Interactive
General Chemistry CD-ROM,
Screen 11.3, Hydrocarbons.

Hydrocarbons

Aliphatic

hydrocarbons

Aromatic

hydrocarbons

Alkanes Cycloalkanes Alkenes Alkynes

Saturated Unsaturated

Figure 27-1 Classification of hydrocarbons.