Basic Organic Nomenclature

An Introduction

Dave Woodcock,
Associate Professor Emeritus UBC (Okanagan)
©1996,2000, 2008

6. Aromatic Compounds

IV Fused-ring Aromatics


Fused-ring aromatic compounds treated here are mainly those with six-membered sp2 hybridized carbon rings joined 1,2 to each other.

Most of these compounds, with up to 5 rings fused have common names which have been accepted into the IUPAC nomenclature system. So, if you need to know them you must learn them!

Ring numbering is shown on the line diagram. Note that only those carbons which can have another atom attached are numbered. Carbons at the fused sites are omitted in the numbering schemes.

There are five sections on this page:

(i) Rings fused in a line.

The two and the three ring compounds have common names.

naphthalene anthracene

From four rings on a systematic name is given using the suffix -cene with a root that is derived from the number of rings fused together.

tetracene pentacene

(ii) Rings fused with one 120 degree angle at or near the centre of the molecule as in the following patterns have a root for the number of rings and the suffix -phene. The first member (3 rings) has the name phenanthrene.
pattern for odd number of rings
pattern for even number of rings

phenanthrene tetraphene
pentaphene hexaphene

(iii) Rings fused in an arc.

benzo[c]phenanthrene dibenzo[c,g]phenanthrene

Note how the molecules with four and more rings in an arc cannot remain flat and become like a spiral. With six and more rings, the overlap of the rings is such that the molecules exist as enantiomers (see next section) in left and right spiral forms stable enough to be isolated.

(vi) Molecules with benzene or naphthalene units in a ring are named with a prefix giving the number of units followed by phenylene (for benzene) or naphthalene.

triphenylene trinaphthalene

(v) Other C-6 fused systems with common names.

pyrene chrysene
picene perylene
coronene ovalene

(vi) Finally a couple of molecules containing rings other than C-6:

acenaphthene azulene

Review Multisubstituted Benzenes

Next page : Stereochemistry. I


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