source: Master Organic Chemistry

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Rules:IUPAC of  unsaturated aliphatic hydrocarbons-

i) Longest chain

The longest chain of carbon  atom (parent chain) is selected as that all double & triple bonds  must be present in parent chain even  it is not the actual longest chain.

ii)   A primary  suffix is added to the root word to indicate the presence of double or triple bond in the parent chain.

For one double bond= Root word +ene

for one triple bond = root word+yne

If parent chain contains two or more double bonds (or triple bonds) the prefixes di, tri, tetra etc. are used before primary suffix .

for two double bonds = Root word + diene

for two triple bonds = Root word + diyne

iii) Numbering of C-Chain-

a)  The parent chain is numbered in a way  that lowest number  is given to that carbon atom linked by double or triple bond.

b) If alkyl groups  are present then preference should be given to double or triple bond because in priority table multiple bond is placed above than alkyl group.

c) The position of multiple bond is indicated by the number  of the first carbon atom involved in the multiple bond. The number  may be indicated either just before the  root word or before the primary  suffix.


iv) Alkyl groups or other substituents are numbered , named & placed in alphabetical order.

v) If  both double & triple bonds are situated at identical position in relation to the end of parent chain, then double bond is given the preference  over the  triple bond.

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