Aromatic Rings

1
Aromatic Rings

• Organic Chemistry
• Some slides adapted from Timberlakes LecturePLUS
  Chem Modules
• http//www.karentimberlake.com/chemodul.htm

2
Hydrocarbon Rings

• OBJECTIVES
• Identify common cyclic ring structures.
• Explain resonance in terms of the aromatic ring
  of benzene.

3
Cyclic Hydrocarbons

• The two ends of the carbon chain are attached in
  a ring in a cyclic hydrocarbon
• -named as cyclo- ____
• hydrocarbon compounds that do NOT contain rings
  are known as aliphatic compounds

4
Aromatic Hydrocarbons

• A special group of unsaturated cyclic
  hydrocarbons is known as arenes
• contain single rings, or groups of rings
• originally called aromatic hydrocarbons,
  because of pleasant odor
• simplest arene is benzene (C6H6)
• Term aromatic applies to materials with bonding
  like that of benzene

5
Aromatic Compounds and Benzene

• Aromatic compounds contain benzene.
• Benzene, C6H6 , is represented as a six carbon
  ring with 3 double bonds.
• Two possible structures can be drawn to show
  benzene in this form. (Called resonance!)

6
Benzene Structure

• The structures for benzene can also be written
  as a single structure where the alternating
  double bonds are written as a circle within the
  ring.
• Benzene
• structure

7
Aromatic Compounds in Nature and Health

• Many aromatic compounds are common in nature and
  in medicine.

8
Naming Aromatic Compounds

• Aromatic compounds are named with benzene as the
  parent chain. One side group is named in front of
  the name benzene.
• methylbenzene chlorobenzene
• (toluene)

9
Naming Aromatic Compounds

• When two groups are attached to benzene, the
  ring is numbered to give the lower numbers to the
  side groups. The prefixes ortho (1,2), meta
  (1,3-) and para (1,4-) are also used.

10
Some Common Names

• Some substituted benzene rings also use a common
  name. Then naming with additional more side
  groups uses the ortho-, meta-, para- system.

11
More prefixes

• Can use
• ortho for 1,2
• meta for 1,3
• para for 1,4

12
Review

• Select the names for each structure
• 1. Chlorocyclohexane
• 2. Chlorobenzene
• 3. 1-chlorobenzene
• 1. Meta-methyltoluene
• 2. Meta-dimethylbenzene
• 3. 1,3-dimethylbenzene

13
Solution

• Select the names for each structure
• 2. Chlorobenzene
• 1. Meta-methyltoluene
• 2. Meta-dimethylbenzene
• 3. 1,3-dimethylbenzene

14
Review

• Write the structural formulas for each of the
  following
• A. 1,3-dichlorobenzene
• B. Ortho-chlorotoluene

15
Solution

• Write the structural formulas for each of the
  following
• A. 1,3-dichlorobenzene
• B. Ortho-chlorotoluene