IUPAC nomenclature Rule for Alkyne (1) Select the longest carbon chain containing a triple bond (2) The numbering of the carbon chain is in such a way that the carbon attached to the triple bond should get the lowest possible number (3) The numbering of the triple bond carbon should be mentioned in the nomenclature (4) All other rules of substituents are the same as alkanes and alkenes ethyne 1-propyne 5-methyl-2-hexyne Nomenclature of cycloalkynes: Nomenclature is according to the suffix = cycloalkyne 4-methyl cyclopentyne cyclohexyne 3-methyl cyclobutyne IUPAC nomenclature Rule for Compounds containing both double and triple bonds (1) If the organic compound contains both double and triple bond, then select the longest carbon chain in such a way that the sum of the carbons attached to the double and triple bond should get the lowest possible number. 1-hexene-3-yne 1 + 3 = 4 (Correct numbering - small sum total) 3 + 5 = 8 (Incorrect numbering - large sum total) (2) Nomenclature is always according to the alkene followed by alkyne i.e. Prefix = alkene, Suffix = alkyne (3) If the sum of the carbons attached to double and triple bond is the same (for both LHS to RHS and RHS to LHS), then select the longest carbon chain in such a way that carbon attached to the double bond should get the lowest possible number 1-butene-3-yne 1 + 3 = 4 (Correct numbering - small sum total) 1 + 3 = 4 (Correct numbering - small sum total) (4) Numbering from LHS to RHS is correct because double bond carbon gets the lower possible number .