Introductory IUPAC Organic Nomenclature

Polyenes

• The root name is based on the longest chain containing both ends of all the alkene units.
• The chain is numbered so as to give the one of the alkene units the lowest possible number (i.e. first point of difference).
• The locant for the lowest numbered carbon of each alkyne is used in the name.
• The appropriate multiplier (i.e. di- for two, tri for three) is inserted before the -yne suffix.
• In order make the name pronounceable,  -a- is inserted after the root.

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- 1,3-butadiene or buta-1,3-diene	CH2=CHH=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)-1,3-pentadiene or (E)-penta-1,3-diene	CH3CH=CHH=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-methyl-1,4-pentadiene or 2-methylpenta-1,4-diene	CH3C(CH3)=CHH=CH2

©Dr. Ian Hunt, Department of Chemistry