Module 1   

Lesson 2.1  Introducing Benzene



Key Concepts


The molecular formula for benzene is C6H6, but its structural diagram is much more complex. In fact, the unique structure of benzene puzzled scientists for years because the molecule displayed properties that were very difficult to explain. For example, benzene has a relatively high melting point and boiling point and demonstrates chemical reactions similar to an alkane.


X-ray diffraction demonstrates that benzene's carbon-carbon bond lengths are all the same; however, they are neither single nor double bonds. In other words, six unbonded electrons are shared equally around a ring structure.

 Read through pages 381 to 382 in your textbook to learn more about the evidence that eventually led to the development of a structure that accurately represented benzene. Study Figure 2 at the bottom of page 381. You will see how models of benzene evolved over the years until scientists arrived eventually at the following line structural diagram.

Fig. 1 Benzene

Learning Tip

Aromatic compounds are not classified as either saturated or unsaturated.


The inner circle illustrates that there are not three specific double bond locations; rather, the six valence electrons appear to be shared equally among the six carbon atoms.


Although the above diagram of benzene is the most widely used, sometimes you will see benzene depicted in a manner that shows the carbon and hydrogen atoms.

Fig. 2  Benzene

Check Your Understanding


Go to your textbook and complete Section 9.4 Questions 1, 7, 8, and 9 on page 385.


Check your work by clicking the banner beneath.

Page 385 Section 9.4 Question 1
Benzene, C6H6, is the simplest aromatic compound. Its carbon-carbon bond lengths are all the same, but they are neither single nor double bonds. Each pair of carbons shares one electron pair, and the six remaining valence electrons are shared around the ring.

Page 385 Section 9.4 Question 7
  1. aliphatic
  2. aromatic
  3. aliphatic
  4. aliphatic
  5. aromatic
  6. aromatic


Page 385 Section 9.4 Question 8
  1. unsaturated
  2. saturated
  3. unclassified*
  4. unsaturated
  5. unsaturated
  6. unclassified*

* Recall that aromatics are classified neither as saturated nor unsaturated.

Page 385 Section 9.4 Question 9
Cyclohex-1,3,5-triene is misleading and incorrect because the physical and chemical properties of benzene suggest it has no double bonds as such.