﻿ Polyenes
 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.
• 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 alkene is used in the name.
• The appropriate multiplier (i.e. di- for two, tri for three) is inserted before the -ene suffix.
• In order make the name pronounceable,  -a- is inserted after the root.
• If there is more than one C=C that can be E/Z, then the location needs to be included with the locants and listed in numerical order, e.g. (2E,4Z)-
• Or, if using cis/trans- then the terms are listed in locant order e.g. trans,cis-
 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 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 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 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

 ©Dr. Ian Hunt, Department of Chemistry