Nomenclature of Aromatic Hydrocarbons

Benzene is the most common aromatic parent structure.

a. The benzene ring is named as a phenyl group when it is a substituent.

phenylethyne

b. Multiple substituents on a benzene ring are numbered to give these substituents the lowest possible numbers. When only two substituents are attached to a benzene ring, they can be named by the common nomenclature using ortho (o-) (1-2 placement), meta (m-) (1-3 placement) or para (p-) (1-4 placement).

Try to name the following compounds using both conventions...

J

  J

* Try to draw structures for the following compounds...

1,2,4-trimethylbenzene J

p-dimethylbenzene J

c. Some common names involving benzene rings that you should know are...

toluene

ortho-xylene

Try to draw structures for the following compounds...

meta-xylene J

para-xylene J

biphenyl...Notice the numbering convention for this compound.

Try to draw a structure for the following compound...

 2,3'-dimethylbiphenyl J

 benzyl group

styrene

polystyrene

 

d. Polycyclic aromatic hydrocarbons that you should know are...

naphthalene

A common nomenclature if only one substituent is on the naphthalene ring system involves the use of alpha and beta.

* Try to name the following compounds using both conventions...

J

J

* Try to draw structures for the following compounds...

a -isopropylnaphthalene J

1-ethyl-5-methylnaphthalene J

anthracene

phenanthrene

e. The annulenes are large aromatic rings that have 4n + 2 p electrons in a cyclic conjugated system (n = any whole number including zero). The compound 1,3,5,7-cyclooctatetraene is not an annulene. It has eight p electrons which would yield 1.5 for "n".

10-annulene

Copyright August 2000 by Richard C. Banks...all rights reserved.