Hydrocarbon Rings
Chemistry 122/121
Cyclic Hydrocarbons
Both saturated and unsaturated
hydrocarbons may be found in the form
of a ring
 The resulting structure has two less
hydrogen than its straight chain
counterpart

◦ Butane = C4H10
◦ Cyclobutane = C4H8
Aromatic Hydrocarbons
Historically, these compounds all had an
odor associated with them
 They may contain a single ring or group of
rings
 Benzene is the simplest aromatic

◦ all examples of aromatics have a structure
comparable to benzene

Another name for them are arenes
The Structure of Benzene
Benzene is a six carbon ring with a
hydrogen atom attached to each carbon
 This leaves each carbon available to make
a double bond
 A maximum of three double bonds can
form within the ring
 As a result, two diagrams can be written
to represent all the places a double bond
can exist within benzene
 Page 710

Resonance
As a result of double bonds being found
in more than one place, the bonding ebetween carbon atoms are shared evenly
around the ring
 Resonance allows the structure to be
more stable
 Benzene is less reactive than its alkene
counterpart

Substituted Aromatic Hydrocarbons
Compounds that contain substituents
attached to a benzene ring are called
derivatives of benzene
 When the benzene ring is the substituent,
it is called a phenyl group
 Benzene rings that have two substituents
are called disubstituted benzenes
 The positions of the substituents can be
in the 1, 2 (ortho), 1,3 (meta), or 1,4
(para) position

For the remainder of class…

Complete Guided Reading 22.4

Practice Problems – use to review

Interpreting Graphics – 22.4