Basic IUPAC Organic Nomenclature

Benzene as a substituent

• In some cases, the benzene ring needs to be treated as a substituent. 
  
• In these cases, the term phenyl, is used to designate the presence of C₆H₅- as a substituent.
• Take care not to confuse terminology (it will be discussed on the next page)
  
•  benzyl substituent = C₆H₅CH₂
•  phenol a compound = C₆H₅OH
•  phenyl substituent = C₆H₅
• The method should be used when the benzene ring is a substituent of the root (the root contains the principle functional group).

Principle functional group is an alkene therefore suffix = -ene The longest continuous chain is C2 therefore root = eth The benzene ring is a substituent therefore = phenyl Location of the phenyl group is unambiguous phenylethene	C6H5CH=CH2
Principle functional group is an alkene therefore suffix = -ene The longest continuous chain is C3 therefore root = prop The benzene ring is a substituent therefore = phenyl Numbering from the right as drawn to give the alkene the lowest locant = 1 Phenyl locant = 3 3-phenylpropene	C6H5CH2CH=CH2
Principle functional group is an alcohol therefore suffix = -ol Hydrocarbon structure is an alkane therefore -an- The longest continuous chain is C2 therefore root = eth The benzene ring is a substituent therefore = phenyl Numbering from the right as drawn to give the -OH the lowest locant = 1 Phenyl locant = 2 2-phenylethanol	C6H5CH2CH2OH

©Dr. Ian Hunt, Department of Chemistry