25.2 Hydrocarbon Rings
25.2 Hydrocarbon Rings
Lesson Objectives
- Describe and name cyclic hydrocarbons.
- Explain how ring strain contributes to the shape of cyclic hydrocarbons. Describe the two primary conforma-
tions of cyclohexane. - Relate the concept of electron delocalization to the structure of benzene.
- Name and write structural formulas for substituted benzene compounds.
Lesson Vocabulary
- cyclic hydrocarbon
- cycloalkane
- cycloalkene
- cycloalkyne
- delocalized electrons
Check Your Understanding
Recalling Prior Knowledge
- What are alkanes?
- What is the difference between a sigma bond and a pi bond?
In the last lesson, you learned about straight-chain and branched hydrocarbons. In this lesson, you will see that
hydrocarbons can also form cyclic structures.
Cyclic Hydrocarbons
Acyclic hydrocarbonis a hydrocarbon in which the carbon chain forms a ring. Acycloalkaneis a cyclic
hydrocarbon in which all of the carbon-carbon bonds are single bonds. Like other alkanes, cycloalkanes are
saturated compounds. Cycloalkanes have the general formula of CnH 2 n. The simplest cycloalkane is cyclopropane,
a three-carbon ring (Figure25.8).
The structural formulas of cyclic hydrocarbons can be represented in multiple ways, two of which are shown above.
Each atom can be shown, as in the structure on the left. However, a convenient shorthand is to omit the element
symbols and only show the shape, as in the triangle on the right. Carbon atoms are understood to be the vertices of
the triangle.