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Basic IUPAC Organic Nomenclature

Polyenes

The term polyene simply implies the presence of several alkenes. To be more specific, a diene has two C=C, a triene has 3 C=C etc.
Polyenes are named in a similar manner to alkenes themselves.
  • Functional group is an alkene, therefore suffix = -ene
  • There are two alkenes, so insert the multiplier di
  • The longest continuous chain is C4 therefore root plus "a" = buta
  • The C=C units are both at the ends so we can number from either end
  • Locants for C=C units are therefore 1- and 3-
buta-1,3-diene
or
1,3-butadiene

butadiene

CH2=CHCH=CH2
  • Functional group is an alkene, therefore suffix = -ene
  • There are two alkenes, so insert the multiplier di
  • The longest continuous chain is C5 therefore root plus "a" = penta
  • The first point of difference requires that we number from the right as drawn
  • Locants for C=C units are therefore 1- and 3-
  • The C3=C4 alkene has E stereochemistry
(E)-penta-1,3-diene
or
(E)-1,3-pentadiene
pentadiene

CH3CH=CHCH=CH2
  • Functional group is an alkene, therefore suffix = -ene
  • There are two alkenes, so insert the multiplier di
  • The longest continuous chain is C5 therefore root plus "a" = penta
  • The substituent is a C1 alkyl group i.e. a methyl group
  • The first point of difference doesn't distinguish the C=C
  • So, need to apply the first point of difference to the alkyl substituent.
  • The first point of difference requires that we number from the left as drawn
  • The methyl group locant is 2-
  • Therefore the locants for C=C units are 1- and 4-
2-methylpenta-1,4-diene
or
2-methyl-1,4-pentadiene
subs pentadiene

CH3C(CH3)=CHCH=CH2
  • Functional group is an alkene, therefore suffix = -ene
  • There are two alkenes, so insert the multiplier di
  • The longest continuous chain is C7 therefore root plus "a" = hepta
  • The first point of difference requires that we number from the left as drawn
  • Therefore the locants for C=C units are 2- and 4-
  • The C2=C3 alkene has E stereochemistry
  • The C4=C5 alkene has Z stereochemistry

(2E,4Z)-hepta-2,4-diene
or
trans,cis-hepta-2,4-diene

hepta-2,4-diene


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