Aromatic Nomenclature

1
Aromatic Nomenclature

• Naming substituted benzenes

2
Monosubstituted Benzenes

• Monosubstituted aromatics are named using
  -benzene as the parent name preceded
  by the substituent name (as a prefix all one
  word)

fluorobenzene nitrobenzene
ethylbenzene
3
Alkyl-substituted Benzenes

• Alkyl substituted benzenes are named according
  to the length of the carbon chain of the
  alkyl group.
• With six carbons or fewer in the alkyl chain,
  they are named as alkylbenzene.
• e.g., propylbenzene

4
Alkyl-substituted Benzenes

• With more than six carbons in the alkyl chain,
  they are named as a phenylalkane, where the
  benzene ring is named as a substituent (phenyl)
  on the alkane chain
• e.g., 4-phenylnonane

4-phenylnonane
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Common Names of Subs. Benzenes

• There are a number of nonsystematic (common)
  names commonly used for certain monosubstituted
  benzenes
• These common names should be memorized.
• These common names are used as base names when
  naming di- or trisubstituted aromatic compounds
  derived from them.

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Common Names of Subs. Benzenes
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The Benzyl Group

• The benzyl group is a common name for a methyl
  substituted benzene (toluene) having substitution
  for one of the hydrogens on the methyl group.
• e.g., benzylbromide

the benzyl group benzylbromide
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Disubstituted Benzenes

• Disubstituted benzenes can be named in one of two
  ways. Each method describes the relative
  positions of the two groups on the benzene ring.
• Systematic numbering of the aromatic ring.
• Using the prefixes ortho-, meta-, or para-.
• The common names for monosubstituted benzenes are
  used as parent (base) names for disubstituted
  aromatics.
• When numbering the ring carbons, carbon 1 is
  always carbon bearing a substituent. If one of
  the substituents changes the base name, the
  carbon bearing that group is carbon 1.

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Disubstituted Benzenes

• ortho- o- 1,2-disubstituted
• (two groups on adjacent carbons on the ring)

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Disubstituted Benzenes

• meta- m- 1,3-disubstituted
• (two groups having one unsubstituted carbon
  between them)

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Disubstituted Benzenes

• para- p- 1,4-disubstituted
• (two groups on opposite sides of the ring)

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Disubstituted Benzenes

• When one of the substituents changes the base
  name, o-, m-, and p- can be used to indicate the
  position of the other substituent.

4
1
3
2
2
1
p-bromoaniline or 4-bromoaniline
o-chlorophenol or 2-chlorophenol
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Common Names of Disubs. Benzenes

• There are a few nonsystematic (common) names for
  disubstituted benzenes that you should be
  familiar with

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Polysubstituted Benzenes

• Polysubstituted benzenes are named by numbering
  the position of each substituent on the ring
  (with more than two substituents, numbering must
  be used rather than o-, m-, and p-.)
• The numbering is carried out to give the
  substituents the lowest possible numbers.
• Carbon 1 is always a carbon bearing a
  substituent.
• For rings with common names, the carbon bearing
  the substituent responsible for the common name
  is always carbon 1.

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Polysubstituted Benzenes

• The ring is numbered in a direction to encounter
  the next substituent with the lowest number.
• The substitutents are listed in alphabetical
  order when writing the name.
• Common names of the monosubstituted benzenes are
  used as parent names for polysubstituted
  aromatics.

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Polysubstituted Benzenes
4
1
3
2
3
2
5
1
4
4-bromo-2-ethyl-1-nitrobenzene
5-bromo-2-chlorophenol
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Polysubstituted Benzenes
2
1
1
2
3
6
3
4
6
5
5
4
2-bromo-6-chloro-4-nitrotoluene
1-bromo-3-chloro-2-ethyl-5-nitrobenzene
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Polycyclic Aromatic Hydrocarbons (PAH)
Metabolic byproducts of benzo a pyrene react
with DNA to form adducts, leading to
carcinogenesis (cancer).