Bridgehead and junction atoms are excluded to avoid ambiguity. 1. 20a-Homoporphyrin 2. Skeletal Replacement of Ring-expanded Systems. Replacement prefixes with appropriate locants are added in front of the name of the ring-expanded porphyrin. Note General practice varies in related areas such as steroids and natural products as to the relative placement of ring modifying and skeletal replacement prefixes.
Further study is needed.
Because atom 19 is a bridgehead, the locant 19a may be ambiguous. 10 and Fig. 11 respectively. Other ring-contracted porphyrins are named systematically according to the rules for naming heterocycles. As for skeletal replacement in porphyrins, replacement of saturated nitrogen atoms of corrin and corrole precede replacement of the unsaturated nitrogen atoms. See TP-1.5 .