The parent chain must contain the multiple bond regardless of the fact whether it also denotes the longest continuous chain of carbon atoms or not. For example, in structure (I), the parent chain consists of five carbon atoms while the longest continuous chain contains six carbon atoms.
If both double and triple bonds are present, the numbering of the parent chain should always be done from that end which is nearer to the double or the triple bond, i.e., the lowest locant rule for the multiple bonds must be followed. For example,
If, however, there is a choice in numbering, the double bond is always given preference over the triple bond. For example,
According to the latest convention (1993 recommendations) while naming unsaturated hydrocarbons, the locant of the double bond or that of the triple bond is placed immediately before the suffix 'ene' or the 'yne' and not before the word root as was the practice being followed earlier. For example,
If however, both double and triple bonds are present in the compound, their locants are placed immediately before their respective suffixes and the terminal *e* from the suffix 'ene' is omitted while writing its complete name.
