Organic Chemistry Lecture: Benzene Nomenclature

Introduction to Benzene

• Benzene molecular formula: C6H6
• High degree of resonance

Monosubstituted Benzene Naming

• Isopropylbenzene: Benzene ring with an isopropyl group
  • Name: Isopropylbenzene
• Nitrobenzene: Benzene with a nitro group
• Chlorobenzene: Benzene with a chlorine atom

Common Names for Monosubstituted Benzenes

• Toluene: Benzene with a methyl group
  • Abbreviations: PHCH3 or PHNE
• Phenol: Benzene with an OH group
• Aniline: Benzene with an NH2 group
• Benzoic acid: Benzene with a carboxylic acid group
• Notable: Students may be expected to memorize 4-10 common names

Disubstituted Benzene Nomenclature

• Ortho Position: Substituents next to each other (adjacent)
• Meta Position: Substituents separated by one carbon
• Para Position: Substituents on opposite sides of the ring
• Example: Bromo, chloro benzene in the meta position (m-bromo-chlorobenzene)
  • Use lowercase letters: o, m, p

Polysubstituted Benzene Nomenclature

• Name the parent chain: benzene
• List substituents alphabetically: bromo, chloro, fluoro
• Number the ring for lowest possible numbering
• Example: 4-bromo-1-chloro-2-fluorobenzene

Common Name Usage

• Toluene Example: Common name used
  • Carbon 1 is the toluene group
  • Example: 4-bromo-2-chloro-toluene

Use of Phenyl and Benzyl

• Phenyl Group: Benzene as a substituent
• Benzyl Group: CH2 group followed by benzene
• Use phenyl for complex parent chains to simplify naming

Complex Nomenclature

• Example: 3-phenyl-1,7-octadiene
• Avoid overly complex benzene naming
  • Example: Phenyl is preferred for simplicity

Conclusion

• Code word for the day: Phenyl
• Phenyl saves time in nomenclature
• Additional discussion in lectures and exams