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Basic IUPAC Organic Nomenclature

Alkenes

Nomenclature
Formula
3D structure
Functional group suffix = -ene

Substituent name = alkenyl

Structural unit :  alkenes contain C=C bonds.
alkene
  • Functional group is an alkene, therefore suffix = -ene
  • The longest continuous chain is C3 therefore root = prop
  • In order to give the alkene the lowest number, number from the right as drawn
  • The C=C is unambiguously between C1 and C2 therefore the locant isn't required
 propene


propene

CH3CH=CH2
  • Functional group is an alkene, therefore suffix = -ene
  • The longest continuous chain is C4 therefore root = but
  • The C=C is between C2 and C3 so the locant is 2-
 but-2-ene or 2-butene


but-2-ene

 CH3CH=CHCH3
  • Functional group is an alkene, therefore suffix = -ene
  • The longest continuous chain is C4 therefore root = but
  • In order to give the alkene the lowest number, number from the right as drawn
  • The C=C is between C1 and C2 so the locant is 1-
 but-1-ene or 1-butene


but-1-ene

 CH3CH2CH=CH2
  • Functional group is an alkene, therefore suffix = -ene
  • The longest continuous chain is C6 therefore root = hex
  • The system is cyclic there prefix = cyclo
  • The C=C is unambiguously between C1 and C2 therefore the locant isn't required.
cyclohexene
cyclohexene

  • Functional group is an alkene, therefore suffix = -ene
  • The longest continuous chain is C5 therefore root = pent
  • In order to give the alkene the lowest number, number from the right as drawn
  • The C=C is between C2 and C3 so the locant is  2-
  • The substituent is a C1 alkyl group i.e. a methyl group
  • The methyl group locant is 4-
4-methylpent-2-ene or 4-methyl-2-pentene
4-methylpent-2-ene



  • Functional group is an alkene, therefore suffix = -ene
  • The longest continuous chain is C6 therefore root = hex
  • The C=C is between C3 and C4 so the locant is  3-
  • The substituent is a C1 alkyl group i.e. a methyl group
  • The first point of difference rule requires numbering from the right as drawn to make the methyl group locant 3-
 3-methylhex-3-ene or 3-methyl-3-hexene
3-methyl-3-hexene




organic chemistry ©Dr. Ian Hunt, Department of Chemistry University of Calgary