The parent chain is the longest continuous chain of carbon atoms in a molecule, taken as the basis for the systematic name. For an alkene or alkyne the rule is modified so that the chosen chain must be the longest one that contains the multiple bond. It matters because the parent chain fixes the root name and the numbering, while all other groups are then cited as substituents attached to it.

主链是分子中最长的连续碳链,作为系统命名的基础。对于烯烃或炔烃,规则有所修改:所选链必须是含有该多重键的最长链。它之所以重要,是因为主链确定了名称词根和编号方式,而所有其他基团随后都作为连接在其上的取代基来标出。