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

Answer:

Here is my understanding of the rules.

Explanation:

  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

Consider

#"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
3,3-dipropylpent-1-en-4-yne.

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