If both double bond and triple bond exist while naming a compound according to IUPAC system, to whom should i give importance first ?

1 Answer
Jul 3, 2017


Here is my understanding of the rules.


  1. Choose the longest continuous chain of carbon atoms, whether or not it contains multiple bonds.

  2. If there is a choice, choose the chain with more multiple bonds.

  3. Number from the end of a chain that is closest to a multiple bond.

  4. If there is a choice, the double bond gets priority.

  5. "Ene" comes before "yne" in the name, no matter what the locants (numbers) are.

Example 1


#"H"_2stackrelcolor(blue)(1)("C")"=CH-CH"_2"-"stackrelcolor(blue)(4)("C")"≡CH"# and #"H"_2"C""="stackrelcolor(blue)(4)("C")"H-CH"_2"-""C""≡"stackrelcolor(blue)(1)("C")"H"#

The correct name is pent-1-en-4-yne.

Example 2

#"H"stackrelcolor(blue)(1)("C")"≡C-"stackrelcolor(blue)(3)("C")"H=CH-CH"_3# is pent-3-en-1-yne.

Example 3

Example 3

Under the "old" IUPAC rules, the above compound would b

Under the "new" rules, the correct IUPAC name is 4-ethenyl-4-ethynylheptane.