For example, in case of vinyl polymers, polymerization should occur at the double bonds and, in some cases, at the triple bond. Using the atom mappings, the nucleophilic atom is selected as head by convention. In the case where the electrophilic atom occurs in the same organic function, which is the case in vinyl polymerization, the tail is selected from the same organic function. In polyamides, the tail atom is located within a different organic function.